Method and apparatus for cutting high quality internal features and contours

ABSTRACT

An automated method for cutting a plurality of hole features using a plasma arc torch system can be implemented on a computer numerical controller. The automated method can include the steps of: a) cutting a lead-in for a hole feature using a lead-in command speed based on a diameter of that hole feature and b) cutting a perimeter for the hole feature using a perimeter command speed greater than the corresponding lead-in command speed for the hole feature. The automated method can also include the step c) of repeating steps a) and b) for each additional hole feature having a same diameter or a different diameter.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of and claims the benefitof U.S. patent application Ser. No. 12/557,920 filed on Sep. 11, 2009,which is a continuation-in-part of U.S. patent application Ser. No.12/466,786 filed on May 15, 2009, and which is also acontinuation-in-part of U.S. patent application Ser. No. 12/341,731filed on Dec. 22, 2008, which applications are owned by the assignee ofthe instant application and the disclosures of which applications areincorporated herein by reference in their entirety. U.S. patentapplication Ser. No. 12/466,786 claims benefit of and priority to U.S.Provisional Patent Application No. 61/154,259 filed on Feb. 20, 2009,which is owned by the assignee of the instant application and thedisclosure of which is also incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The invention relates generally to plasma arc cutting torch systems.More specifically, the invention relates to a method and apparatus forcutting internal features and contours in a workpiece using a plasmatorch tip configuration.

BACKGROUND OF THE INVENTION

Plasma cutting uses a constricted electric arc to heat a gas flow to theplasma state. The energy from the high temperature plasma flow locallymelts the workpiece. The energy from the high temperature plasma flowlocally melts the workpiece. For many cutting processes, a secondary gasflow (also known as a shield gas flow, or shield flow) is used toprotect the torch and assist the cutting process. The momentum of thehigh temperature plasma flow and the shield flow help remove the moltenmaterial, leaving a channel in the workpiece known as a cut kerf(“kerf”).

Relative motion between the plasma torch and the workpiece allows theprocess to be used to effectively cut the workpiece. The shield gasinteracts with the plasma gas and the surface of the workpiece and playsa critical role in the cutting process. Downstream of the nozzleorifice, the plasma and shield gas flows come into contact enabling heatand mass transfer.

FIG. 1 is a diagram of a known automated plasma torch system. Automatedtorch system 10 can include a cutting table 22 and torch 24. An exampleof a torch that can be used in an automated system is the HPR260 autogas system, manufactured by Hypertherm, Inc., of Hanover, N.H. The torchheight controller 18 can be mounted to a gantry 26. The automated system10 can also include a drive system 20. The torch is powered by a powersupply 14. The plasma arc torch system can also include a gas console 16that can be used to regulate/configure the gas composition (e.g., gastypes for the shield gas and plasma gas) and the gas flow rates for theplasma arc torch. An automated torch system 10 can also include acomputer numeric controller 12 (CNC), for example, a HyperthermAutomation Voyager, manufactured by Hypertherm, Inc., Hanover, N.H. TheCNC 12 can include a display screen 13 which is used by the torchoperator to input or read information that the CNC 12 uses to determineoperating parameters. In some embodiments, operating parameters caninclude cut speed, torch height, and plasma and shield gas composition.The display screen 13 can also be used by the operator to manually inputoperating parameters. A torch 24 can also include a torch body (notshown) and torch consumables that are mounted to the front end of atorch body. Further discussion of CNC 12 configuration can be found inU.S. Patent Publication No. 2006/0108333, assigned to Hypertherm, Inc.,the disclosure of which is incorporated herein by reference in itsentirety.

FIG. 2 is a cross-sectional view of a known plasma arc torch tipconfiguration, including consumable parts and gas flows. The electrode27, nozzle 28, and shield 29 are nested together such that the plasmagas 30 flows between the exterior of the electrode and the interiorsurface of the nozzle. A plasma chamber 32 is defined between theelectrode 27 and nozzle 28. A plasma arc 31 is formed in the plasmachamber 32. The plasma arc 31 exits the torch tip through a plasmanozzle orifice 33 in the front end of the nozzle to cut the workpiece37. The shield gas 34 flows between the exterior surface of the nozzleand the interior surface of the shield. The shield gas 34 exits thetorch tip through the shield exit orifice 35 in the front end of theshield, and can be configured to surround the plasma arc. In someinstances, the shield gas also exits the torch tip through bleed holes36 disposed within the shield 29. A portion of the shield gas flow canenter the cut kerf with the plasma gas and form a boundary layer betweenthe cutting arc and the workpiece surface 37. The composition of thisboundary layer influences the heat transfer from the arc to theworkpiece surface and the chemical reactions that occur at the workpiecesurface. An example of plasma torch consumables are the consumable partsmanufactured by Hypertherm, Inc., of Hanover, N.H. for HPR 130 systems,for cutting mild steel with a current of 80 amps. The nozzle 28 can be avented nozzle, (e.g., comprising an inner and outer nozzle piece and abypass channel formed between the inner and outer nozzle pieces directsthe bypass flow to atmosphere), as described in U.S. Pat. No. 5,317,126entitled “Nozzle And Method Of Operation For A Plasma Arc Torch” issuedto Couch et al., which is owned by the assignee of the instantapplication and the disclosure of which is incorporated herein byreference in its entirety.

Internal features (e.g., hole features, substantially circular holes,slots, etc.) cut with plasma arc torches using known methods can resultin defects, such as, for example, protrusions, divots, “bevel” or“taper.” Bevel or taper is where a feature size at a bottom side of theworkpiece is smaller than the feature size at the top side of the plate.For example, the diameter of an internal feature (e.g., a hole/holefeature) at the top of the workpiece should be cut to match the size ofa bolt to pass through the internal feature. If a hole feature hasdefects, such as, protrusions, divots, bevel or taper, the defects inthe hole feature can cause the hole feature diameter to vary from thetop of a workpiece to the bottom of the workpiece. Such defects canprevent the bolt from passing through the bottom of the workpiece.Secondary processes, such are reaming or drilling are required toenlarge the diameter of the bolt hole feature at the bottom of theworkpiece. This prior method of ensuring hole cut quality can be timeconsuming, suggesting that a more efficient method of cutting holes andcontours in a single workpiece is needed.

Numerous gas mixtures can be used for both plasma and shield gas inplasma cutting processes. For example, oxygen is used as the plasma gasand air as the shield gas for the processing of mild steel. Some lowcurrent processes (e.g., less than 65 A) use oxygen as both the plasmagas and shield gas to cut thin material (e.g., workpieces less than 10gauge). The oxygen plasma gas/air shield gas combination is popular formild steel at arc currents above 50 amps, due to the ability to producelarge parts with good quality and minimal dross at high cutting speeds.Such cutting processes have certain drawbacks. For example, though theoxygen plasma gas/air shield gas configuration can cleanly cut largesections with straight edges (e.g., contours), such a gas combination isunable to cut high quality hole features. Instead, hole features cutwith oxygen plasma gas and air shield gas has a substantial bevel or“taper”.

Traditionally, to correct defects in the hole feature, such as, forexample, a “protrusion” (e.g., excess material) where the lead-in of acut transitions into a perimeter of the cut, the arc is left on aftercutting the perimeter to “clean up” the defect left by the lead-in bycutting the unwanted excess material. This process is called “overburn.” Over burning, however, can result in removing too much material,leaving an even larger defect (e.g., leaving a divot in place of theprotrusion).

SUMMARY OF THE INVENTION

The present invention substantially improves the cut quality for smallinternal part features (e.g., hole features) cut from a workpiece usinga plasma arc torch while maintaining the productivity and cut qualityfor large features, or contours. Hole features (e.g., holes) cut usingplasma arc torches using known methods can result in defects, such asprotrusions (e.g., where not enough material was cut, leaving excessmaterial), divots (e.g., where too much material was cut), bevel and/ortaper, which can prevent, for example, a bolt from passing through thebottom of a workpiece. Cutting parameters (e.g., gas composition,cutting speed, cutting current, etc.) can be manipulated to improve thecut quality of a small internal part feature while still maintainingquality for large features or contours. The shield gas composition canaffect the taper, or bevel, of the edge of a hole cut that is beingperformed. For example, a first shield gas composition can be used whencutting the contour, and a second, different, shield gas composition canbe used when cutting one or more holes or small internal feature in asingle workpiece while using a single plasma torch consumableconfiguration.

The cutting speed of the “lead-in” of the cut can affect the cut qualityfor the hole feature. Using the same speed for the lead-in of the cut asthe rest of the cut can result in defects such as protrusions, where thelead of the cut transitions into the perimeter. As noted above,traditionally, an “over burn” process can be used to remove the excessmaterial; however, an over burn process can remove too much material,leaving behind a defect, such as a divot. Using a low N₂ gas composition(e.g., a gas composition of O₂ plasma gas and O₂ shield gas) can also beused to cut small internal features to help minimize the bevel and/ortaper. Cutting a workpiece using, for example air, is not as sensitiveto defects as cutting with O₂ gas. Using O₂ plasma and O₂ shield gas canfurther amplify defects such as protrusions and/or divots in the holefeature. By changing the shield gas composition when cutting a hole andwhen cutting a contour in a single workpiece, the need for secondaryprocesses can be eliminated. While laser cutting systems can yield highquality cuts, plasma arc torch systems provide a low cost alternative tocutting internal features (e.g., hole features).

In one aspect, the invention features an automated method for cutting aplurality of hole features using a plasma arc torch system, theautomated method implemented on a computer numerical controller. Theautomated method can include the following steps: a) cutting a lead-infor a hole feature using a lead-in command speed based on a diameter ofthat hole feature and b) cutting a perimeter for the hole feature usinga perimeter command speed greater than the corresponding lead-in commandspeed for the hole feature. The automated method can also include stepc) of repeating steps a) and b) for each additional hole feature havinga same diameter or a different diameter.

In some embodiments, the automated method can include cutting a contourusing a secondary gas composition having a higher nitrogen content thanthe secondary gas composition used to cut the plurality of holefeatures.

In another aspect, the invention features an automated method forcutting a plurality of hole features in a workpiece with a plasma arctorch, each hole feature including a lead-in portion, a hole perimeterportion, and a lead-out portion. The method can include cutting a firsthole feature in a workpiece having a first diameter by cutting a firstlead-in using a first command speed and increasing a command speed fromthe first command speed to a second command speed after cutting thefirst lead-in to cut at least a portion of the first hole perimeter. Themethod can also include cutting a second hole feature in the workpiecehaving a second diameter greater than the first diameter by cutting asecond lead-in using a third command speed, the third command speedgreater than the first command speed and increasing the command speedfrom the third command speed to a fourth command speed after cutting thesecond lead-in to cut at least a portion of the second hole perimeter.

In some embodiments, the fourth command speed and the second commandspeed are substantially the same. The automated method can also includethe steps of cutting the first hole feature in the workpiece using afirst secondary gas flow, cutting the second hole feature in theworkpiece using a second secondary gas flow and cutting a contour in theworkpiece using a third secondary gas flow having a higher nitrogencontent than the first secondary gas flow or the second secondary gasflow. In some embodiments, the first secondary gas flow and the secondsecondary gas flow have substantially the same gas composition.

In another aspect, the invention features an automated method forcutting a plurality of hole features in a workpiece with a plasma arctorch. The automated method can include cutting a first hole featurehaving a first diameter using a first automated process by initiating asecondary gas flow having a first gas composition and cutting the firsthole feature with a first set of cutting parameters. The automatedmethod also can include cutting a second hole feature having a seconddiameter greater than the first diameter using a second automatedprocess by initiating the secondary gas flow having a second gascomposition and cutting the second hole feature with a second set ofcutting parameters, where at least one parameter of the second set ofcutting parameters is different from the first set of cuttingparameters. The automated method can also include cutting a contourusing a third automated process by initiating the secondary gas flowhaving a third gas composition, the third gas composition having agreater nitrogen content than the first and second gas compositions andcutting the contour with a third set of cutting parameters, where atleast one parameter of the third set of cutting parameters is differentfrom the first or second set of cutting parameters.

The first set of cutting parameters can include a first lead-in commandspeed, a first perimeter command speed and the first gas composition.The second set of cutting parameters can include a second lead-incommand speed, a second perimeter command speed, and the second gascomposition. The third set of cutting parameters can include a contourcommand speed and the third gas composition. The contour command speedcan be greater than the first lead-in command speed, the first perimetercommand speed, the second lead-in command speed and the second perimetercommand speed. The first gas composition and the second gas compositioncan be substantially the same (e.g., the same).

In another aspect, the invention features an automated method forcutting at least a first hole feature and a second hole feature in aworkpiece with a plasma arc torch, the second hole feature larger thanthe first hole feature. The method can include moving the plasma arctorch to a first location and cutting the first hole feature in theworkpiece by cutting a first lead-in by ramping up a cutting speed up toa first lead-in cutting speed, increasing the cutting speed after thefirst lead-in to cut a first perimeter, initiating current ramp downafter an inner kerf edge of the first perimeter substantially intersectsan outer kerf edge of the first lead-in and maintaining or increasingthe cutting speed until a cutting current is extinguished, the cuttingcurrent extinguished at or near where an outer kerf edge of the firstlead-in substantially joins an outer kerf edge of the first perimeter.The method can also include moving the plasma arc torch to a secondlocation and cutting the second hole feature in the workpiece by cuttinga second lead-in by ramping up the cutting speed up to a second lead-incut speed, the second lead-in speed greater than the first lead-in cutspeed, increasing the cutting speed after the second lead-in to cut asecond perimeter, initiating current ramp down after an inner kerf edgeof the second perimeter substantially intersects an outer kerf edge ofthe second lead-in and maintaining or increasing the cutting speed untilthe cutting current is extinguished, the cutting current extinguished ator near where an outer kerf edge of the second lead-in joins an outerkerf edge of the second perimeter.

In some embodiments, current ramp down can be initiated while cuttingthe first hole feature or the second hole feature at a point based on adiameter of the first hole feature or the second hole feature.

In another aspect, the invention features a plasma arc torch systemconfigured to cut contours and a plurality of hole features of varyingsizes in a plurality of workpieces of varying thicknesses. The systemcan include a plasma arc torch having an electrode and a nozzle for acorresponding current level and a computer numerical controller (CNC).The CNC can be configured to select, from a plurality of gascompositions, a first secondary gas composition used to cut holefeatures and a second secondary gas composition used to cut contours.The CNC can also select, from a plurality of perimeter cutting speeds, aperimeter cutting speed based on a material thickness of a workpiece.The CNC can select, from a plurality of lead-in speeds, a lead-in speedbased on a size of a hole feature to be cut and the material thicknessof the workpiece, each perimeter cutting speed greater than eachcorresponding lead-in speed.

The lead-in speed can be proportional to the size of the hole feature tobe cut. The computer numerical controller can be configured to select,from a plurality of negative time offset values, a negative time offsetvalue based on the current level. The negative time offset can be basedon the size of the hole feature to be cut or the current level.

In yet another aspect, the invention features a computer readableproduct, tangibly embodied on an information carrier, and operable on acomputer numeric controller for cutting a plurality of hole features ina workpiece with a plasma arc torch system. The computer readableproduct can include instructions being operable to cause the computernumeric controller to select a shield gas composition having a nitrogencontent lower than air, establish a lead-in cutting speed for a holefeature to be cut, the lead-in cutting speed a function of a diameter ofthe hole feature to be cut, establish a perimeter cutting speed for thehole feature to be cut, the perimeter cutting speed greater than thecorresponding lead-in cutting speed and provide a first command toextinguish a plasma arc, the first command independent of a secondcommand to decelerate a plasma arc torch.

The perimeter cutting speed can be based on a thickness of theworkpiece.

In another aspect, the invention features an automated method forcontrolling a plasma arc torch when cutting a hole feature in aworkpiece. The method can include establishing a first command toextinguish a plasma arc at a first location along a cut, the firstcommand independent of a second command to vary a motion of the plasmaarc torch and establishing a negative time offset associated with thefirst command that determines initiation of a current ramp down at asecond location that precedes the first location along the cut.

The first location can correspond to an intersection between an outerkerf edge of a perimeter of the hole feature and an outer kerf edge of alead-in of the hole feature. Varying the motion of the plasma arc torchcan include decelerating or accelerating the plasma arc torch. Thenegative time offset can be the sum of a delay between the first commandand initiation of the current ramp down and a time between initiation ofthe current ramp down and extinguishment of the plasma arc. In someembodiments, a negative time offset is retrieved from a cut chart. Thenegative time offset can be a function of a diameter of the hole featureor a current level.

In yet another aspect, the invention features an automated method forestablishing cutting parameters for cutting a plurality of hole featureshaving a plurality of hole diameters using a plasma arc torch. Themethod can include establishing a first location corresponding to wherean outer kerf edge of a cut along a perimeter of each hole featuresubstantially joins the outer kerf edge of the cut along a lead-in ofeach hole feature. The method can also include establishing a secondlocation preceding the first location based on a hole diameter of thehole feature being cut or a cutting current level and initiating plasmaarc termination at the second location such that the plasma arc issubstantially extinguished when the plasma arc torch reaches the firstlocation.

In some embodiments, the plurality of hole features are cut in aworkpiece with a given thickness and a distance traveled by the plasmaarc torch between the second location and the first location issubstantially similar for the plurality of hole features. The automatedmethod can also include determining a negative time offset based on thehole diameter of the hole feature being cut, the negative time offsetdetermining initiation of plasma arc termination at the second location.The plurality of hole features having the plurality of hole diameterscan be cut using one set of consumables for the plasma arc torch (e.g.,automated process to cut the hole features without changing theconsumables in the plasma torch). In some embodiments, the workpiece canbe pierced to begin cutting each hole feature.

In one aspect, the invention features a method for cutting an internalfeature, such as a hole feature, in a workpiece using a plasma arctorch. The plasma arc torch can be used to cut along a portion of a pathincluding a first zone, a second zone, and a third zone using a plasmacutting system. The method can include cutting in the first zone usingat least one cutting parameter from a first cutting parameter set, thefirst cutting parameter set including a first cutting current and/or afirst command speed establishing a first torch speed. The method canalso include cutting in the second zone using at least one cuttingparameter from a second cutting parameter set. The second cuttingparameter set can be different from (e.g., where at least one parameterin the set is different) the first cutting parameter set and can includea second cutting current and/or a second command speed establishing asecond torch speed. The method can also include cutting in the thirdzone using at least one cutting parameter from a third cutting parameterset. The third cutting parameter set can be different from the firstcutting parameter set or the second cutting parameter set and caninclude a third cutting current and/or a third command speedestablishing a third torch speed.

The command speed can be a set point for a torch/cutting speed. Thetorch speed can be the command speed offset by anacceleration/deceleration of the torch to reach the command speedsetpoint and inefficiencies/limitations inherent in the plasma arc torchsystem.

In some embodiments, the first zone corresponds to a lead-in of a cut,the second zone corresponds to a perimeter of the cut, and the thirdzone corresponds to a kerf break-in region of the cut. The hole featurecan be defined, at least in part, by an outer kerf edge of a cut in thesecond zone and at least a portion of an outer kerf edge of a cut in thethird zone. Cutting in the first zone can include cutting a semi-circlein the workpiece.

The second command speed can be greater than the first command speed. Insome embodiments, the third cutting current is less than the secondcutting current during at least a portion of the third zone.

In one aspect, the invention features a method for cutting an internalfeature, such as a hole feature, in a workpiece along at least a portionof a path including a first zone and a second zone using a plasmacutting system. The method can include the steps of initiating a plasmagas flow, initiating a current flow to ignite a pilot arc, transferringthe arc to the workpiece and piercing the workpiece (e.g., to begincutting an internal feature in the workpiece). The method can includecutting in the first zone using a first command speed establishing afirst torch speed and cutting in the second zone using a second commandspeed establishing a second torch speed. The second command speed can begreater than the first command speed.

The internal feature (e.g., hole feature) can be a substantiallycircular hole or a slot.

The path can include a third zone. The first zone can correspond to alead-in of a cut, the second zone can correspond to a perimeter of thecut, and the third zone can correspond to a kerf break-in region of thecut. The method can also include ramping down a cutting current in thethird zone such that the cutting current reaching substantially zeroamperes at a location corresponding to a beginning of the second zonewhere the first zone, second zone and third zone substantiallyintersect. The cutting current can be ramped down at a rate based, atleast in part, upon a length between a beginning of the third zone andthe beginning of the second zone.

The first command speed can be based at least in part on a diameter ofthe hole feature. The torch speed can be reduced after the cuttingcurrent reaches substantially zero amperes. A third command speed can beused, for example, to cut in the third zone. The third command speed candefine a third torch speed. A ramp down of the cutting current can beinitiated at a location in the third zone determined by the third torchspeed and a ramp down time (e.g., the time required for the current toreach substantially zero amperes).

The method can include cutting in the first zone or in the second zoneusing a gas flow composition comprising O2 plasma gas and O2 shield gas.

In another aspect, the invention features a method for cutting aninternal feature (e.g., a hole feature) in a workpiece along at least aportion of a path including a first zone, a second zone, and a thirdzone using a plasma cutting system. The method can include the steps ofinitiating a plasma gas flow, initiating a current flow to ignite apilot arc, transferring the arc to the workpiece and piercing theworkpiece (e.g., to begin cutting an internal feature/hole feature inthe workpiece). The method can include cutting in a first zone and asecond zone. The command speed of a cut for the second zone can bedifferent than a command speed of a cut in the first zone. The methodcan also include reducing a cutting current in the third zone such thatthe cutting current reaches substantially zero amperes at a point wherean outer kerf edge of a cut in the third zone substantially meets anouter kerf edge of the cut in the first zone. The method can alsoinclude decelerating a torch speed of the plasma cutting system afterthe cutting current has reached substantially zero amperes.

In some embodiments, the method can include cutting in the second zonewith a command speed greater than the command speed of the cut in thefirst zone.

A distance from a center of the hole feature to an outer kerf edge ofthe cut in the second zone can be substantially similar to a distancefrom the center of the hole feature to an outer kerf edge of the cut inthe third zone at a point where the first and third zone intersect. Thehole feature can be substantially defined by an outer kerf edge of thecut in the second zone and at least a portion of the outer kerf edge ofthe cut in the third zone. In some embodiments, the first zonecorresponds to a lead-in of the cut, the second zone corresponds to aperimeter of the cut and the third zone corresponds to a kerf break-inregion of the cut.

The torch speed can be decelerated after a point where the outer kerfedge of the cut in the first zone substantially intersects with theouter kerf edge of the cut in the third zone. The torch speed can bedecelerated to reach zero at a predetermined distance after the pointwhere the outer kerf edge of the cut in the first zone substantiallyintersects with the outer kerf edge of the cut in the third zone.

In some embodiments, the cutting current in the third zone can be rampeddown such that the cutting current reaches substantially zero amperes ata location where an outer kerf edge of the cut in the first zonesubstantially intersects with an outer kerf edge of the cut in the thirdzone.

In another aspect, the invention features a method for cutting aninternal feature (e.g., a hole feature) in a workpiece along at least aportion of a path including a first zone, a second zone, and a thirdzone and using a plasma cutting system. The method can include the stepsof initiating a plasma gas flow, initiating a current flow to ignite apilot arc, transferring the arc to the workpiece and piercing theworkpiece (e.g., to begin cutting an internal feature/hole feature inthe workpiece). The method can include cutting in the second zone with acommand speed different from a command speed of the first zone of thecut. The method can also include ramping down a cutting current in thethird zone to remove a diminishing material such that an outer kerf edgeof a cut in the third zone substantially aligns with an outer kerf edgeof a cut in the second zone. The method can include decelerating a torchspeed of the plasma cutting system after the cutting current has reachedsubstantially zero amperes.

In some embodiments, the cutting current can be ramped down in the thirdzone so that the cutting current reaches substantially zero ampereswhere the outer kerf edge of the cut in the third zone intersects withthe outer kerf edge of a cut in the first zone. The diminishing materialcan be defined at least in part by an outer kerf edge of the cut in thefirst zone and an outer kerf edge of the cut in the third zone. In someembodiments, the third zone can be cut with a command speed greater thanthe command speed of the second zone of the cut.

In yet another aspect, the invention features a method for cutting aninternal feature (e.g., a hole feature) in a workpiece using a plasmacutting system that reduces defects in the hole feature. The method caninclude the steps of initiating a plasma gas flow, initiating a currentflow to ignite a pilot arc, transferring the arc to the workpiece andpiercing the workpiece at the beginning of a cut (e.g., to cut aninternal feature/hole feature in the workpiece). The method can includeestablishing a cutting arc and a cut speed with respect to the workpieceand increasing the cut speed to a second cut speed after a first pointin a hole cut path. The method can also include ramping down a cuttingcurrent after a second point in the hole cut path without reducing thecut speed. The second cut speed can be maintained until the cuttingcurrent reaches substantially zero amperes. The second cut speed canalso be increased to a third cut speed before the cutting currentreaches substantially zero amperes.

The first zone can define a lead-in of a cut and the second zone candefine at least a portion of a perimeter of the hole feature.

In some embodiments, the step of increasing the cut speed can includecutting in a first zone of the hole cut path with a first command speedand cutting in a second zone of the hole cut path with a second commandspeed greater than the first command speed. The first command speed canbe based on a diameter of the hole feature.

The cutting current can be reduced (i.e., ramp down of the cuttingcurrent initiated) after the second point in the hole cut path and thecutting arc can be extinguished substantially near the first point inthe hole cut path. In some embodiments, the torch can cut from thesecond point in the hole cut path and return back to the first point inthe hole cut path to form the hole feature in the workpiece. The cuttingcurrent can be ramped down while cutting from the second point in thehole cut path back to the first point in the hole cut path.

In another aspect, the invention features a plasma arc torch system forcutting an internal feature (e.g., a hole feature) in a workpiece alongat least a portion of a path including a first zone, a second zone, anda third zone. The plasma arc torch system can include a plasma torchincluding an electrode and a nozzle, a lead that provides a cuttingcurrent to the plasma arc torch, a gantry attached to the plasma torchthat moves the plasma torch and a computer numerical controller thatcontrols cutting parameters of the plasma arc torch in the first zone,the second zone, and the third zone. The computer numerical controllercan establish a first command speed for the first zone and a secondcommand speed for the second zone. The first command speed can be based,at least part, on a diameter of the hole feature. The second commandspeed can be greater than the first command speed. The computernumerical controller can also establish a third cutting current for thethird zone. The third cutting current can ramp down so that the thirdcutting current reaches substantially zero amperes where an outer kerfedge of a cut in the first zone substantially intersects with an outerkerf edge of a cut in the third zone.

The computer numerical controller can include a look-up table toidentify the cutting parameters of the plasma arc torch.

The third cutting current can ramp down to remove a diminishing material(e.g., the remaining material of the workpiece to finish cutting thehole feature) so that an outer kerf edge of the cut in the third zonesubstantially aligns with an outer kerf edge of a cut in the secondzone.

In yet another aspect, the invention features a computer readableproduct, tangibly embodied on an information carrier, and operable on acomputer numeric controller for a plasma arc torch cutting system. Thecomputer readable product can include instructions being operable tocause the computer numeric controller to select cutting parameters forcutting an internal feature (e.g., a hole feature) in a workpiece alongat least a portion of a path comprising a first zone, a second zone, anda third zone. The cutting parameters can include a first command speedfor the first zone based, at least part, on a diameter of the holefeature and a second command speed for the second zone of the cut. Thesecond command speed can be greater than the first command speed. Thecutting parameters can also include a third cutting current for thethird zone, where the third cutting current ramps down such that thethird cutting current reaches substantially zero amperes where an outerkerf edge of a cut in the first zone substantially intersects with anouter kerf edge of a cut in the third zone.

The third cutting current can ramp down to remove a diminishing material(e.g., the remaining material of the workpiece to finish cutting thehole feature) so that an outer kerf edge of the cut in the third zonesubstantially aligns with an outer kerf edge of a cut in the secondzone.

In another aspect, the invention features a method for cutting aninternal feature (e.g., a hole feature) in a workpiece using a plasmaarc torch to reduce defects in the hole feature. The plasma arc torchcan cut along at least a portion of a path including a first zone, asecond zone and a third zone. The method can include selecting one of aplurality of cutting current ramp down operations for cutting in thethird zone, where each of the plurality of cutting current ramp downoperations is a function of a diameter of the hole feature. The methodcan also include extinguishing the plasma cutting current when a torchhead passes from the third zone to the second zone at a location wherethe first zone, second zone and third zone substantially intersect. Themethod can also include substantially maintaining or increasing a torchspeed in the third zone until the torch head passes from the third zoneinto the second zone.

In another aspect, the invention features a method for cutting aninternal feature (e.g., a hole feature) in a workpiece using a plasmaarc torch to reduce defects in the hole feature. The plasma arc torchcan cut along at least a portion of a path including a first zone, asecond zone and a third zone. The method can include the steps ofinitiating a plasma gas flow, initiating a current flow to ignite apilot arc, transferring the arc to the workpiece and piercing theworkpiece (e.g., to begin cutting an internal feature/hole feature inthe workpiece). The method can include cutting alone the first zone andthe second zone of the path. A ramp down of a cutting current can beinitiated at a first point in the third zone such that the cuttingcurrent is extinguished at a second point where the first zone, thesecond zone and the third zone substantially intersect. The first pointin the third zone can be determined based on a ramp down time of thecutting current. The method can also include the step of deceleratingthe plasma arc torch so that a torch speed reaches substantially zero ata predetermined distance after the second point.

In some embodiments, the predetermined distance is about ¼ of an inch.In some embodiments, the predetermined distance is about ¼ of an inchwhere an upper limit of the hole cutting speed is about 55 ipm and alower limit for a table acceleration is about 5 mG.

In another aspect, the invention features a method for cutting a holefeature in a workpiece along at least a portion of a path using a plasmacutting system. The path can include a first zone and a second zone. Themethod can include the steps of initiating a plasma gas flow, initiatinga current flow to ignite a pilot arc, transferring the arc to theworkpiece and piercing the workpiece (e.g., to begin cutting an internalfeature/hole feature in the workpiece). The method can include cuttingin the first zone using a first command speed (e.g., establishing afirst torch speed), where the first command speed is part of anacceleration curve (e.g., programmed for a plasma arc torch system). Themethod can include cutting in the second zone using a second commandspeed (e.g., establishing a second torch speed), where the secondcommand speed is part of the acceleration curve and is also greater thanthe first command speed.

In yet another aspect, the invention features a method for cutting ahole feature in a workpiece along at least a portion of a path using aplasma cutting system. The path can include a first zone and a secondzone. The method can include the steps of initiating a plasma gas flow,initiating a current flow to ignite a pilot arc, transferring the arc tothe workpiece and piercing the workpiece (e.g., to begin cutting aninternal feature/hole feature in the workpiece). The method can includecutting where the first zone and the second zone substantially intersect(e.g., where the lead-in of the cut transitions into the perimeter ofthe cut) at a first torch speed. The method can also include cutting atleast a portion of the second zone at a second torch speed, where thesecond torch speed is greater than the first torch speed.

In one aspect, the invention features a method for cutting a hole and acontour in a workpiece with a plasma torch. In one embodiment the methodincludes a plasma torch including a nozzle and electrode that define aplasma chamber; a plasma arc is generated in the plasma chamber. In oneembodiment, the plasma torch also includes a shield gas supply line forproviding a shield gas flow to the plasma arc torch, and a control unitfor controlling cutting parameters including cutting speed and shieldgas composition. In one embodiment the method includes controlling thecutting parameters such that when the contour is cut the shield gascomprises a first shield gas composition and when the hole is cut theshield gas comprises a second shield gas composition. In someembodiments, the first shield gas composition is different than thesecond shield gas composition.

In still another aspect the invention features a method for improvingthe cutting characteristics of a small internal feature in a plasmatorch cutting operation. In one embodiment the method includes the stepsof cutting a small internal feature using a second shield gascomposition, the small internal feature positioned within theanticipated contour cut of a workpiece, and cutting a contourcorresponding to the anticipated contour cut using a first shield gascomposition.

In a further aspect the invention features a method for cutting a holeand a contour in a workpiece using a plasma arc torch. The plasma arctorch can include a nozzle and electrode that define a plasma chamber,such that a plasma arc generated in the plasma chamber is used to cutthe workpiece, and a shield gas supply line that delivers a shield gasflow to the plasma torch. In one embodiment, the method includes thestep of cutting a hole in a workpiece wherein the shield gas flowcomprises a second shield gas composition which is selected such that abevel of an edge of the hole is substantially eliminated. In oneembodiment the method can also include the steps of cutting a contourwherein the shield gas flow comprises a first shield gas composition,and controlling the first shield gas composition and the second shieldgas composition such that while cutting the hole the second shield gascomposition comprises less nitrogen than the first shield gascomposition.

In another aspect, the invention features a further method of cutting ahole in a workpiece using a plasma arc torch. The method can include aplasma arc torch including high-current consumables, the high-currentconsumables including a nozzle and electrode that define a plasmachamber. In one embodiment the method can also include the steps ofgenerating a plasma arc in the plasma chamber using an arc current above50 amps, and controlling a shield gas composition of a shield gas flowsuch that when the hole is being cut the shield gas compositioncomprises an amount of nitrogen such that any potential bevel of theside wall of the hole is substantially eliminated.

The invention features, in one aspect, a plasma torch system for cuttinga hole and contour in a workpiece. In one embodiment the plasma torchsystem includes a plasma torch tip configuration including a nozzle andan electrode that defines a plasma chamber, a plasma arc is generated inthe plasma chamber. In one embodiment the plasma torch system alsoincludes a shield gas supply line for providing a shield gas flow to theplasma torch tip and a control unit for controlling a composition of theshield gas flow. In one embodiment the control unit controls thecomposition of the shield gas flow such that while cutting the contourthe shield gas flow comprises a first shield gas composition and whilecutting the hole the shield gas flow comprises a second shield gascomposition. In one embodiment the improvement comprises a computerreadable product tangibly embodied in an information carrier, operableon the control unit, the computer readable product containing cuttinginformation for the plasma arc torch system including instructions thatselect the first shield gas composition when cutting the contour andselect the second shield gas composition when cutting the hole.

In another aspect, the invention features a component that includes acomputer readable product tangibly embodied in an information carrier,operable on a CNC for use in a plasma torch system. In one embodimentthe computer readable product includes cutting information for cutting ahole and a contour from a workpiece using a plasma arc torch, includinginstructions such that while cutting the hole a shield gas flowcomprises a second shield gas composition and when the contour is cutthe shield gas flow comprises a first shield gas composition.

In still another aspect, the invention features a computer numericalcontroller for controlling cutting parameters of a plasma torchincluding a composition of a shield gas flow. In one embodiment thecontroller includes a processor, an electronic storage device, aninterface for providing control instructions to a plasma arc torch, anda look up table for selecting the composition of the shield gas flow forthe plasma torch. In one embodiment the controller controls thecomposition of the shield gas flow according to whether the plasma torchwill cut a hole or a contour in a workpiece.

Any of the aspects above can include one or more of the followingfeatures. The second shield gas composition can comprise less nitrogenthan the first shield gas composition such that a bevel of an edge ofthe hole is substantially eliminated. In some embodiments the workpieceis mild steel, in some embodiments the first shield gas composition isair, and in some embodiments the second shield gas composition isoxygen. The second shield gas composition can also consist essentiallyof oxygen during hole cutting. In one embodiment a flow rate of theshield gas flow is reduced during hole cutting. A cutting speed of thetorch can be reduced during hole cutting. In one embodiment, controllingthe cutting parameters can further comprise controlling the secondshield gas composition according to a ratio of a diameter of the hole toa thickness of the workpiece. The ratio can be less than or equal to2.5. In some embodiments the ratio is less than or equal to 1. In someembodiments the ratio is less than or equal to 0.7 and/or limited by thesize of the pierce penetration.

Any of the aspects above can also include one or more of the followingfeatures. In one embodiment controlling the cutting parameters caninclude current ramping sequences for arc termination where the rampingis constant for both contour cutting and hole cutting. The step ofcontrolling the cutting parameters can also further comprise controllingan amount of nitrogen in the shield gas flow such that the second shieldgas composition contained less nitrogen as a percentage of the totalvolume than the first shield gas composition whereby a bevel of an edgeof the hole is substantially reduced.

Any of the aspects above can also include one or more of the followingfeatures. In one embodiment a method can include the step of providing acomputer readable product tangibly embodied in an information carrier,operable on a CNC for use with a plasma torch system, the computerreadable product containing cutting information for the plasma arc torchincluding instructions that select the first shield gas composition whencutting the contour and select the second shield gas composition whencutting the hole. In some embodiments the second shield gas compositioncan be selected according to a ratio of the diameter of the hole to thethickness of a workpiece. And in some embodiments the cuttinginformation include instructions such that when a hole is cut thecontrol unit controls the second shield gas composition according to aratio of a diameter of the hole to a thickness of the workpiece.

One advantage is the capability to produce high quality plasma cutholes, while maintaining productivity and dross levels typicallyachieved on contour cuts. Another advantage is the minimization ofimpact on overall part cost by limiting the use of more expensive shieldgas mixtures to short duration hole cuts. A further advantage is greatertime efficiency by allowing the operator to use a single configurationof torch consumables when cutting holes and contours in a singleworkpiece, while simultaneously preventing the quality deteriorationseen when using the prior cutting technique of a single shield gas forboth hole and contour cutting.

Other aspects and advantages of the invention can become apparent fromthe following drawings and description, all of which illustrate theprinciples of the invention, by way of example only.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of the invention described above, together with furtheradvantages, may be better understood by referring to the followingdescription taken in conjunction with the accompanying drawings. Thedrawings are not necessarily to scale, emphasis instead generally beingplaced upon illustrating the principles of the invention.

FIG. 1 is a diagram of a known mechanized plasma arc torch system.

FIG. 2 is a cross sectional view of a known plasma arc torch tip.

FIG. 3 is a sample workpiece showing anticipated hole and contour cutoutlines, according to an illustrative embodiment.

FIG. 4 is an illustration of tolerance measurements used to determinecylindricity of a hole.

FIG. 5 is a block diagram of a plasma arc torch system with a proposedgas system, according to an illustrative embodiment.

FIG. 6A is a schematic showing a first zone of a path followed by aplasma arc torch head, according to an illustrative embodiment of theinvention.

FIG. 6B is a schematic showing a second zone of the path followed by aplasma arc torch head, according to an illustrative embodiment of theinvention.

FIG. 6C is a schematic showing a third zone of the path followed by aplasma arc torch head, according to an illustrative embodiment of theinvention.

FIG. 6D is a schematic showing a fourth zone of followed by a plasma arctorch head, according to an illustrative embodiment of the invention.

FIG. 6E shows a method for cutting a hole feature from a workpiece,according to an illustrative embodiment of the invention.

FIG. 6F shows a method for cutting a hole feature from a workpiece,according to another illustrative embodiment of the invention.

FIG. 7A shows a straight lead-in shape for cutting a hole feature,according to an illustrative embodiment of the invention.

FIG. 7B shows a quarter circle lead-in shape for cutting a hole feature,according to an illustrative embodiment of the invention.

FIG. 7C shows a semi-circle lead-in shape for cutting a hole feature,according to an illustrative embodiment of the invention.

FIG. 8A shows a top view of a hole feature where a first zone of a pathfor cutting a workpiece is straight, according to an illustrativeembodiment of the invention.

FIG. 8B shows a bottom view of the hole feature from FIG. 8A, accordingto an illustrative embodiment of the invention.

FIG. 8C shows a top view of a hole feature where a first zone of a pathfor cutting a workpiece is a semi-circle shape, according to anillustrative embodiment of the invention.

FIG. 8D shows a bottom view of the hole feature from FIG. 8C, accordingto an illustrative embodiment of the invention.

FIG. 9 is a graph showing measured deviations for different lead-incommand speeds, according to an illustrative embodiment of theinvention.

FIG. 10 is an exemplary look-up chart for lead-in command speeds,according to an illustrative embodiment of the invention.

FIG. 11 is a schematic of a portion of a hole cut path, according to anillustrative embodiment of the invention.

FIG. 12 is a graph showing a cutting current and a command speed as afunction of time, according to an illustrative embodiment of theinvention.

FIG. 13 is an exemplary look-up chart for cutting parameters, accordingto an illustrative embodiment of the invention.

FIG. 14 is a graph showing measured deviations for a hole feature,according to an illustrative embodiment of the invention.

FIG. 15 shows a method for operating a plasma arc torch to cut a holefeature from a workpiece, according to an illustrative embodiment of theinvention.

FIG. 16 is a graph showing hole quality results for holes cut fromdifferent processes.

FIG. 17 is a flow diagram that shows how gas flows can be manipulatedaccording to an illustrative embodiment of the invention.

FIG. 18 is a table illustrating different gas combinations for cuttingmild steel, according to an illustrative embodiment of the invention.

FIG. 19A is a cross section of a hole cut with the prior art cuttingprocess.

FIG. 19B is a cross section of a hole cut according to an illustrativeembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

A “hole feature” (e.g., hole) can be defined as a shape having adiameter (or dimension) to workpiece (plate) thickness ratio ofapproximately 2.5 or smaller. FIG. 3, by way of example, shows a 6×6inch square piece of 0.5 inch thick plate steel 100 that in oneembodiment, could be cut from a larger workpiece (not shown). A one inchdiameter hole feature 105 in the 0.5 inch thick plate of steel 100 wouldhave a ratio of 2. A hole/hole feature, as used herein, can becategorized as a small internal part features that are not necessarilyround, but where a majority of the features have dimension that areabout 2.5 times or less than the thickness of the materials (e.g., a 1inch square 110 in the ½ inch plate steel 100). Features such as“contours” can include both straight 115 or curved 120 cuts.

As noted above, hole features cut using prior art methods can result indefects, such as divots (e.g., too much material taken), protrusions(e.g., not enough material taken), “bevel” or “taper”. Bevel can bemeasured by the cylindricity of the completed hole cut. Cylindricity isdefined as a tolerance zone that is established by two concentriccylinders between which the surface of a cylindrical hole must lie asillustrated in FIG. 4. In FIG. 4 the tolerance zone can be defined asthe space between the two arrows 81. The smaller the tolerance zone, themore the surface represents a “perfect” cylinder. A large taper or bevelin a hole feature, on the other hand, will result in a large tolerancezone. Cylindricity of a hole feature can also be measured using acoordinate-measuring machine (“CMM”). For example, the hole featuresurface (e.g., encompassing taper, protrusions, or divots) of the holefeature can be measured near of the top 71, middle 72, and bottom 73 ofthe edge 74 of the hole feature. This measurement data is used to formconcentric cylinders defining the cylindricity of the hole feature. Theradial difference between the concentric cylinders is illustrated by thespace between the arrows 81.

An exemplary torch system configuration that can be used to cut features(e.g., hole features, contours, etc.) is shown in FIG. 5. FIG. 5 is ablock diagram of an exemplary plasma arc torch system including anautomatic gas control system according to an embodiment of theinvention. The plasma torch system can include all of the elementsdescribed above in connection with FIG. 1. Additionally, the torchsystem can include a gas console 40 that provides plasma and shield gas(e.g., secondary gas) to the plasma arc torch 41. The plasma gas and theshield gas flows from the gas console 40 through gas supply lines 42 to,in some embodiments, a gas selection consol 45 and a gas metering consol44 allows for the mixing of different types of gases, before the gasmixture continues to the plasma torch 41. The gas selection consol 45allows the selection and mixing of one of a plurality gases, theselected gases can then be metered by the gas metering console 44. Thegas consol can receive gas inputs including, for example, oxygen,nitrogen, F5, H35, H5, and air. The gas metering consol 44 can thenmeasure the plasma gas and shield gas. This control configuration allowsfor the plasma system to rapidly change the required shield gas or gasmixture for hole piercing, hole cutting, or contour cutting. Forexample, when cutting a hole feature the gas consol 40 can provide airas the shield gas during the piercing process and when the piercing ofthe metal plate is complete, the gas consol 40 can automatically switchthe shield gas to O₂ for hole cutting. When the plasma system moves tocut a contour, the gas consol 40 can switch the shield gas back to airas the shield gas for both the piercing and cutting processes. Suchrapid switching can be directed by code or programming in the CNC 12. Inone embodiment, the shield gas composition for cutting a hole is O₂. Insome embodiments, the shield gas composition selected when cutting ahole feature contains less nitrogen than the shield gas composition usedwhen cutting a contour. In some embodiments, the shield gas compositionused when cutting a hole feature can include He, N₂, O₂, or combinationsthereof.

The gas supply line 42 configured to carry the shield gas flow can bereferred to as shield gas supply line 42A in some embodiments. And insome embodiments, the gas supply line that carry plasma gas flow arereferred to as plasma gas supply line 42B. In some embodiments, thecomposition of the plasma gas flow is controlled using valves 47. Insome embodiments the valves 47 are on-off solenoid valves, and in someembodiments the valves are variable solenoid valves. In someembodiments, the plasma and shield gas (e.g., secondary gas) can be O₂,Air, He, N₂ or some combination thereof The gas metering console 44 canalso include a venting valve 48 which can also be an on/off valve or asolenoid valve. In some embodiments, the vent valve 48 is used to enablerapid switching of the plasma gas and shield gas.

The CNC 12 can be any computer that controls a plasma torch system. ACNC 12 can have a processor, electronic storage device, and an interfacefor providing control instructions to a plasma arc torch. The storagedevice can be internal or external and can contain data relating to thepart to be cut in the workpiece. In other embodiments, the CNC 12 can bemanually programmed, and in some embodiments the CNC 12 can include acomputer readable product that includes computer readable instructionsthat can select or configure operating parameters of the plasma torchsystem.

Reproduced below are exemplary computer readable instructions for a CNC12.

The exemplary instructions below correspond to a round hole feature cutinto a square contour cut using a Hypertherm Automation Voyager CNCcontroller with an HPR 260 Autogas Console, all manufactured byHypertherm, Inc. of Hanover, N.H. The exemplary code below, used withthe Hypertherm Automation CNC controllers, provides two separate cutcharts for the hole (G59 V503 F1.01 through G59 V507 F31) and for thecontour (G59 V503 F1 through G59 V507 F31). Other forms of code, orcomputer readable instructions, can be used with one or more cut chartsto provide a similar, or even identical final output. Notably, the leftcolumn in the exemplary code below contains the referenced code lines;the right column provides general a generic explanation of theinstructions contained in each code line.

G20 English units are sets G91 Incremental programming mode G59 V503F1.01 Load a custom cut chart for a hole G59 V504 F130 ″ G59 V505 F3 ″G59 V507 F31 ″ G00X1.7500Y-1.7500 Move to hole center M07 Plasma startG03X-0.0970I-0.0485 Hole motion G03X0.0015Y0.0168I0.0970 ″G03X0.0212Y-0.0792I0.0955J- ″ 0.0168 M08 Plasma stop G59 V503 F1 Loadcut chart for contour cut G59 V504 F130 ″ G59 V505 F2 ″ G59 V507 F31 ″G00X-1.6757Y1.5624 Move to contour start location M07 Plasma startG01X0.2500 Contour motion G01X3.0000 ″ G01Y-3.0000 ″ G01X-3.0000 ″G01Y3.0000 ″ G01Y0.2500 ″ M08 Plasma stop M02 End of program

In some embodiments, the computer readable products are referred to ascut charts. In some embodiments, the computer readable product (notshown), or cut charts, includes cutting information includinginstructions to select a first shield gas when the torch 41 is cutting acontour in a workpiece and to select a second shield gas compositionwhen the torch is cutting a hole feature in the same workpiece. In someembodiments, the cut chart contains information that selects the shieldgas composition based on the type of cut (e.g., a contour cut or a holefeature cut). In some embodiments, the CNC is able to rapidly switchfrom one shield gas to another depending on the instructions containedin the cut chart. In some embodiments, the torch operator selects theshield gas composition and the CNC 12 only provides signals to control,for example, the plasma gas supply line valves 44 based on theinformation input from the torch operator.

In some embodiments, the torch operator selects a cutting program thatincludes both hole feature and contour cutting instructions. An operatorcan select a hole cut chart and a contour cut chart designed to executeconsecutively. In some embodiments, the hole feature cut will bepositioned within the contour cut anticipated by the CNC 12 on theworkpiece. When a cutting program includes instructions for both holefeature cuts and contour cuts, the cut chart will include furtherinstructions such that the hole feature is cut first using a secondshield gas composition and then the contour cut is cut using a firstshield gas composition. Cutting the hole features first within a profileof the anticipated contour cut prevents movement of the workpiece whilethe hole features are being cut, thus eliminating deviations that wouldoccur if the contour cuts of the part were cut first and the holefeatures cut second.

In other embodiments, the computer readable product is nesting software,such as nesting software made by MTC of Lockport, N.Y. Nesting softwarecan provide code that designates when the first shield and second shieldgases are to be used based upon CAD drawings of the part to be cut. Thenesting software can use the CAD drawing to identify the hole featuresor small internal features based upon the ratio of a hole featurediameter to the thickness of the workpiece. The nesting software canthen provide instructions to the CNC 12 so that the first shield gas isused when cutting contours and the second shield gas is used whencutting hole features. Alternatively, the CNC can include software thatselects the appropriate shield gas, for hole feature cutting and contourcutting without being provided instructions from the nesting software.

FIGS. 6A-6C show a path 100 for cutting a hole feature (e.g., asubstantially circular hole or rounded slot) from a workpiece, accordingto an illustrative embodiment of the invention. The path can include atleast three zones: a first zone, a second zone, and a third zone. Theterm “zone(s)” as used herein can be defined to include segments orportions of a cut or travel path of a torch head over a workpiece. Insome embodiments, the path includes a fourth zone. The path can definethe motion of the plasma arc torch (e.g., the torch shown in FIG. 1),regardless of whether the cutting current is running or extinguished(i.e., regardless of whether the plasma arc torch is cutting theworkpiece). For purposes of clarity, the individual zones have beendefined in the figures, however, the transitions between zones (e.g.,the transition from the first zone to the second zone, transition fromthe second zone to the third zone, etc.) is not a precise location, butcan be a buffer type region.

FIG. 6A shows the first zone 110 of the path, which can define a“lead-in” of a cut. The plasma arc torch can cut along the first zone110 from a beginning 120 of the first zone to an end 130 of the firstzone. A cut along the first zone of the path 110 can include acorresponding outer kerf edge 140 and a corresponding inner kerf edge150. In this embodiment, the first zone 110 defines a “semi-circle”shaped lead-in cut. The shape of the first zone 110 (e.g., the shape ofthe lead-in) and the command speed are parameters that can affect thequality of the hole feature cut from the workpiece. The command speedcan be a set point for a torch/cutting speed. The torch speed can bedefined as the command speed offset by an acceleration or decelerationof the torch to reach the command speed setpoint and inefficiencies orlimitations inherent in the plasma arc torch system.

FIG. 6B shows a second zone 160 of the path, which can define aperimeter of the cut (e.g., the hole perimeter and/or the perimeter ofthe hole feature). The plasma arc torch can cut along the second zone160 from a beginning 170 of the second zone 160 to an end 180 of thesecond zone 160. As shown, the torch head can move from the end 130 ofthe first zone 110 into the beginning 170 of the second zone 160. Thecut in the second zone 160 can include a corresponding outer kerf edge190 and a corresponding inner kerf edge 200.

FIG. 6C shows the third zone 210 of the path, which can define a kerfbreak-in region (e.g., “lead-out”) of the cut. The plasma arc torch cancut along the path in the third zone 210 from a beginning 220 of thethird zone 210 to an end 230 of the third zone 210 (e.g., where thefirst zone 110, second zone 160, and third zone 210 substantiallyintersect). As shown, the torch head can move from the end 230 of thethird zone 210 into, for example, a location 240 corresponding back tothe beginning 170 of the second zone 160. The cut in the third zone 210can include a corresponding outer kerf edge 250.

The third zone 210 of the path can begin at or near a point 260 wherethe outer kerf edge 140 of the first zone 110 (e.g., the lead-in)substantially intersects with the inner kerf edge 200 of the second zone160. The point 260 as shown in the figure is approximated, as theleading edge 261 of the kerf (e.g., the leading edge of the cut in thesecond zone 160) would break into the outer kerf edge 140 of the firstzone 110 before the inner kerf edge 200. Therefore, the kerf break-inregion would in fact take place where the leading edge 261 of the kerf(e.g., the leading edge of the cut in the second zone 160) would breakinto the outer kerf edge 140 of the first zone 110. However, forpurposes of clarity, the third zone 210 of the path can be defined tobegin at or near point 260. In this embodiment, the third zone 210 ofthe path ends at or substantially near a “0 degree point” 270corresponding to the location where the outer kerf edge 140 of the firstzone 110 (e.g. the lead-in) substantially intersects with the outer kerfedge 250 of the third zone 210 and/or the outer kerf edge 190 of thebeginning 170 of second zone 160. The ramp down of the current in thethird zone 210 and/or varying the command speed of the torch in thefirst zone 110, second zone 160 or third zone 210 are parameters thatcan affect the quality of the hole feature cut from the workpiece.

In some embodiments, where the hole feature is a circular hole featurewith minimal defects, a distance from a center 280 of the hole featureto an outer kerf edge 190 of the cut in the second zone 160 can besubstantially similar to a distance from the center of the hole featureto an outer kerf edge 250 of the cut in the third zone 210 at a pointwhere the first zone 110 and third zone 210 intersect.

To cut a hole feature from a workpiece, a plasma arc torch can move fromthe first zone 110, to the second zone 160, then to the third zone 210,and then into a fourth zone. The movement of the torch head can follow apath starting from the beginning 120 of the first zone 110, to the end130 of the first zone 110. From the end 130 of the first zone 110, thetorch can move to the beginning 170 of the second zone continuing to theend 180 of the second zone. From the end 180 of the second zone 160, thetorch can move to the beginning 220 of the third zone 210 continuing tothe end 230 of the third zone 210. At the end 230 of the third zone 210,the torch can continue a path 240 that overlaps with the beginning 170of the second zone 160 or to another location on the workpiece. The holefeature can be defined, at least in part, by an outer kerf edge 190 ofthe cut in the second zone 160 and at least a portion of an outer kerfedge 250 of the cut in the third zone 210.

To cut a hole feature in a workpiece, a plasma gas flow can be initiatedand a current flow can be initiated to ignite a pilot arc. The arc canbe transferred to the workpiece. In some embodiments, a plasma arc torchbegins cutting a hole feature in a workpiece by piercing the workpieceat a first location (e.g., a beginning 120 of the first zone 110 orpoint 280) and cuts a semicircle in the workpiece (e.g., a semi-circlepath) along the first zone 110 of the path. The plasma arc torch can cutalong the first zone 110 and “lead-in” to the second zone 160 of thepath and begin cutting the perimeter of the hole feature. The plasma arctorch can cut along the second zone 160 of the path into the third zone210 of the path. In some embodiments, the plasma arc torch cuts alongthe second zone 160 of the path using O₂ plasma gas and O₂ shield gas.The plasma arc torch can cut the workpiece in the third zone 210 whileeither substantially maintaining the command speed of the torch or whileincreasing the command speed of the torch. The plasma arc torch cancontinue to cut the workpiece in the third zone 210 of the path until itreaches at or substantially near a “0 degree point” 270 (e.g., where theouter kerf edge 140 of the first zone 110 (e.g. the lead-in)substantially intersects with the outer kerf edge 250 of the third zone210 and/or the outer kerf edge 190 of the beginning 170 of second zone160). The cutting current can be ramped down in the third zone 210 suchthat the cutting current is extinguished and/or the arc is “shut off”(e.g., the plasma arc torch stops cutting the workpiece) as the plasmaarc torch reaches at or near this “0 degree point” 270 (e.g., the arcshut off point). The torch head can continue moving past the “0 degreepoint” 270 even though the torch is no longer cutting the workpiece.After the torch head reaches the “0 degree point” 270 and after the archas been extinguished, the torch head can be decelerated along a path240. The torch head can be decelerated while moving a path 240 thatoverlaps with the second zone 160. If the torch is decelerated along apath 240 that follows the circular path of the hole feature, as shown inFIG. 6C, the following equations can be used to calculate the “lead-out”motion angle (e.g., the angle traveled by the torch head after the “0degree point” 270 after which the torch is decelerated to a stop) andthe minimum “lead-out” motion length (e.g., the distance traveled by thetorch head after the “0 degree point” 270 after which the torch isdecelerated to a stop):

$\begin{matrix}{L = \frac{V^{2}}{\left( {2 \cdot a} \right)}} & {{EQN}.\mspace{14mu} 1} \\{\Phi = {360 \cdot \frac{L}{\left( {\Pi \cdot D} \right)}}} & {{EQN}.\mspace{14mu} 2}\end{matrix}$where “L” is the minimum lead-out motion length, “V” is the velocity ofthe torch head, “a” is a table deceleration and “D” is the motiondiameter of the hole feature. In some embodiments, the torch head beginsto decelerate only after the current has been extinguished. The minimumlead-out motion length “L” can be defined as the minimum distancerequired between the “0 degree point” 270 and the point where the torchdecelerates to a stop to ensure that the torch does not begindecelerating prior to the “0 degree point” 270. The torch head can becommanded to decelerate to a stop at point 290 a predetermined distanceafter the “0 degree point” 270. In some embodiments, the minimumlead-out motion length is about ¼ of an inch.

FIG. 6D shows a fourth zone 240 or 240′ of a path (e.g., a “decelerationzone”) for a plasma arc torch head, according to an illustrativeembodiment of the invention. As noted above, the plasma arc torch canstop cutting (e.g., the cutting current extinguished) as the plasma arctorch reaches at or substantially near the “0 degree point” 270 (e.g.,where the outer kerf edge 140 of the first zone 110 substantiallyintersects with the outer kerf edge 250 of the third zone 210 and/or theouter kerf edge 190 of the beginning 170 of second zone 160). The plasmaarc torch head can enter a fourth zone 240 or 240′ of the path anddecelerate in the fourth zone.

In some embodiments, the fourth zone 240 substantially overlaps in spacewith a beginning 170 the second zone 160. In some embodiments, the torchhead can travel in the fourth zone 240′ where the path extends toanother location on the workpiece. In some embodiments, the torch headcan be decelerated to a stop at point 290 or 301 located at apredetermined distance (e.g., ¼ of an inch) after the “0 degree point”270 so that the torch does not begin to decelerate until the arc issubstantially extinguished.

A method for cutting a hole feature from a workpiece can include cuttingin the first zone 110 using at least one cutting parameter from a firstcutting parameter set, cutting in the second zone 160 using at least onecutting parameter from a second cutting parameter set, and cutting inthe third zone 210 using at least one cutting parameter from a thirdcutting parameter set. The first cutting parameter set can include afirst cutting current or a first command speed establishing a firsttorch speed. The command speed can be a setpoint for the speed set by auser, CNC, or computer program, etc. The torch/cutting speed can bedefined as the command speed offset by an acceleration/deceleration ofthe torch to reach the command speed setpoint and anyinefficiencies/limitations inherent in the plasma arc torch system. Thesecond cutting parameter set can be different from (e.g., have at leastone parameter different from) the first cutting parameter set and caninclude a second cutting current or a second command speed (e.g.,greater than the first command speed) establishing a second torch speed.The third cutting parameter set can be different from (e.g., have atleast one parameter different from) the first cutting parameter set orthe second cutting parameter set and can include a third cutting current(e.g., less than the second cutting current) or a third command speedestablishing a third torch speed. The first, second and third parametersets can be independent from one another (e.g., the parameters areselected independently of one another).

In some embodiments, no two parameter sets are identical. For example,the plasma arc torch system can change a command speed whentransitioning from the first zone to the second zone (e.g., increase thecommand speed so that the command speed in the second zone is higher). Ahigher command speed (e.g., resulting in a higher torch speed) can beused to cut the second zone (e.g., perimeter) than the first zone (e.g.,lead in) so as to minimize changes in centripetal acceleration andminimize dynamic responses by the arc. If a command speed were to besubstantially maintained between the first zone and the second zone, thecentripetal acceleration in the first zone would be greater than thesecond zone, which can result in dynamic responses by the cutting arcand unwanted defects. The plasma arc torch system can also change acutting current when transitioning from the second zone to the thirdzone (e.g., ramp down the cutting current in the third zone). The plasmaarc torch system can also change the torch speed when transitioning fromthe third zone to the fourth zone (e.g., begin to decelerate the torchafter the cutting current has been extinguished).

FIG. 6E shows a method for cutting a hole feature from a workpiece,according to an illustrative embodiment of the invention. The method caninclude step 310 of cutting in the first zone 110 using a first commandspeed establishing a first torch speed, step 320. The method can alsoinclude cutting in the second zone 160 using a second, different,command speed establishing a second torch speed, such that the torchspeed is increased when moving from the first zone to the second zone.In some embodiments, the first command speed and the second commandspeed are part of an acceleration curve (e.g., where the second commandspeed is greater than the first command speed). In some embodiments, theworkpiece is cut at a first torch speed (e.g., established by a commandspeed) where the first zone and the second zone substantially intersectand a second, greater, torch speed is used to cut at least a portion ofthe second zone (e.g., a majority of the second zone). As noted above,the torch speed can be increased when moving from the first zone to thesecond zone so as to minimize changes in centripetal acceleration anddynamic responses by the cutting arc which can result in unwanteddefects. The method can also include step 330 of ramping down a cuttingcurrent (e.g., reducing a cutting current) in the third zone 210 suchthat the cutting current reaches substantially zero amperes (step 350)at a location/point corresponding to a beginning 170 of the second zone210 where the first zone 110, second zone 160 and third zone 210substantially intersect (e.g., at or substantially near the “0 degreepoint” 270 as shown in FIGS. 6C and 6D). The method can includesubstantially maintaining or further increasing the command speed in thethird zone during ramp down of the current (step 340). The method caninclude decelerating a torch speed of the plasma cutting system afterthe cutting current has reached substantially zero (Step 360).

The command speed of the cut for the second zone 160 can be different(e.g., greater than) than a command speed of the cut in the first zone110. The first command speed can be based at least in part on a diameterof the hole feature. The third zone 210 can be cut with a command speed(e.g., a third command speed) greater than the command speed of thesecond zone 160 of the cut. The torch speed can be decelerated after apoint where the outer kerf edge 140 of the cut in the first zone 110substantially intersects with the outer kerf edge 250 of the cut in thethird zone 210 (e.g., the “0 degree point” 270 as shown in FIGS. 6C and6D). The torch speed (e.g., the actual speed of the torch head) can bedecelerated to reach zero at a predetermined distance after the pointwhere the outer kerf edge 140 of the cut in the first zone 110substantially intersects with the outer kerf edge 250 of the cut in thethird zone 210.

The plasma cutting current in the third zone 210 (e.g., the thirdcutting current) can be extinguished when a torch head passes from thethird zone 210 to the second zone 160 at a location where the first zone110, second zone 160 and third zone 210 substantially intersect. Thecutting current can be reduced (e.g., ramped down) in the third zone 210such that the cutting current reaches substantially zero amperes at apoint/location where an outer kerf edge 250 of the cut in the third zone210 substantially meets an outer kerf edge 140 of the cut in the firstzone 110. The ramp down for the cutting current in the third zone 210can be ramped down at a rate based, at least in part, upon a lengthbetween a beginning 220 of the third zone 210 and the beginning 170 ofthe second zone 160. Alternatively, the rate at which the cuttingcurrent is ramped down can be a function of a diameter of the holefeature to be cut from the workpiece. A ramp down of the cutting currentcan be initiated at a location in the third zone 210 determined by thethird torch speed and a ramp down time (e.g., the time required for thecurrent to reach substantially zero amperes).

The plasma arc torch can cut in the first zone 110, second zone 160,and/or the third zone 210 using a gas flow composition of O2 plasma gasand O2 shield gas (e.g., or low N₂ gas composition) to reduce defectssuch as bevel and/or taper of the hole feature.

A plasma arc torch system (e.g., as shown in FIG. 1) can be used to cuta hole feature in a workpiece along a first zone 110, a second zone 160,and a third zone 210. The plasma arc torch system can include a plasmatorch 24 including an electrode 27 and a nozzle 28, a lead that providesa cutting current to the plasma arc torch 24, a gantry 26 that moves theplasma torch and a CNC 12 that controls cutting parameters of the plasmaarc torch in the first zone 110, the second zone 160, and the third zone210. A CNC 12 can select cutting parameters for cutting a hole featurein a workpiece. A computer readable product, tangibly embodied on aninformation carrier, and operable on a CNC 12, can include instructionsbeing operable to cause the CNC 12 to select the cutting parameters. TheCNC 12 can establish a first command speed for the first zone 110 and asecond command speed for the second zone 160. The first command speedcan be based, at least part, on a diameter of the hole feature. Thesecond command speed can be greater than the first command speed. TheCNC 12 can also establish a third cutting current for the third zone 210and ramp down the third cutting current so that the third cuttingcurrent reaches substantially zero amperes where an outer kerf edge 140of the cut in the first zone 110 substantially intersects with an outerkerf edge 250 of the cut in the third zone 210. The CNC 12 can include alook-up table to identify the cutting parameters of the plasma arctorch.

FIG. 6F shows a method for cutting a hole feature from a workpiece,according to another illustrative embodiment of the invention. FIG. 6Fshows an exemplary movement path followed by a plasma arc torch duringhole cutting, the movement path traced out along the top of a workpiece.First, the plasma gas and shield gas flow can be initiated, along withthe arc current. The initiation of the gas flows and the current arc canvary depending on the consumable and torch configuration being used bythe operator. U.S. Pat. Nos. 5,070,227, 5,166,494, and 5,170,033, allassigned to Hypertherm®, Inc. and incorporated herein by reference intheir entireties, describe various gas flow and current settings thatcan be used during initiation, operation, and shut-down of the plasmaarc, and cutting process. After the plasma arc is initiated, it istransferred to the workpiece. Once the arc is transferred to theworkpiece, in some embodiments, the torch height is lowered using thetorch height controller. A hole cut is begun in a workpiece by firstpiercing the workpiece (e.g., at point 370) using the plasma arc. Oncethe workpiece is pierced through by the plasma arc, the shield gas canbe switched to a shield gas composition optimized for hole cutting. Insome embodiments, the torch will begin to translate across the workpieceto cut the hole feature into the workpiece along the hole cut patternwhich can be, in some embodiments, determined by the part drawing plasmaand shield.

To cut a hole feature from a workpiece, the workpiece can be pierced(e.g., at a piercing position 370) to begin cutting an internalfeature/hole feature in the workpiece. A cutting arc and a cut speed canbe established with respect to the workpiece (e.g., piercing theworkpiece at point 370 and setting a command speed that defines the cutspeed). The cut speed can be increased to a second cut speed after afirst point 380 (e.g., after the end of the first zone as describedabove in FIG. 6A) in a hole cut path. In some embodiments, the plasmaarc torch can cut the workpiece in the third zone so that the amount ofcurrent per linear distance traveled reduces as the torch cuts along thethird zone. A cutting current can be ramped down after a second point390 in the hole cut path (e.g., after the end of the second zone and ator after the beginning of the third zone as described above in FIGS.6B-6C) either while substantially maintaining the cut speed or whileincreasing the cut speed. The plasma arc torch can also substantiallymaintain the cutting current but increase the command speed (e.g.,thereby increasing the torch speed) while cutting in the third zone. Thetorch can cut from the second point 390 in the hole cut path and returnback to the first point 380 in the hole cut path to form the holefeature in the workpiece. The cutting current can be ramped down whilecutting from the second point 390 in the hole cut path back to the firstpoint 380 in the hole cut path. The cutting arc can be extinguishedsubstantially near the first point 380 in the hole cut path (e.g., nearthe “0 degree point” 270 shown in FIGS. 6C-6D). The second cut speed caneither be maintained until the cutting current reaches substantiallyzero amperes or the second cut speed can be increased to a third cutspeed before the cutting current reaches substantially zero amperes(e.g., at or near first point 380).

Any of the techniques described herein can be used to cut two or morefeatures (e.g., hole features 105 and/or contours 115 or 120 as shown inFIG. 3) in a workpiece using an automated method/process. An automatedmethod can be used to cut a plurality of hole features or other features(e.g., contours) using a plasma arc torch. “Automated method” as usedherein implies that the process is performed automatically (e.g., withminimal or no interaction by an operator) by a plasmas arc torch systemusing one set of consumables (e.g., an operator does not need to changeconsumables during the cut).

For example, an automated process can include a step a) of cutting alead-in for a hole feature (e.g., as shown in FIG. 6A) using a lead-incommand speed based on a diameter of that hole feature and step b) ofcutting a perimeter of the hole feature (e.g., as shown in FIG. 6B)using a perimeter command speed greater than the corresponding lead-incommand speed for the hole feature. Steps a) and b) can be automaticallyrepeated for each additional hole feature having a same diameter or adifferent diameter. The automated process can also include cutting oneor more contours in addition to the hole features. A contour (e.g.,features 115 or 120 shown in FIG. 3) can be cut using a secondary gascomposition (e.g., via the gas control system of FIG. 5) having a highernitrogen content than the secondary gas composition used to cut theplurality of hole features.

In another embodiment, a first hole feature having a first diameter anda second hole feature having a second diameter greater than the firstdiameter, can be cut using an automated process (e.g., automatically cutby a plasma arc torch using one set of consumables, without changingconsumables). Each hole feature can include a lead-in portion (e.g.,first zone of FIG. 6A), a hole perimeter portion (e.g., second zone ofFIG. 6B), and a lead-out portion (e.g., third zone of FIG. 6C). By wayof example, a first hole feature can be cut using a first command speedand increasing a command speed from the first command speed to a secondcommand speed after cutting the first lead-in to cut at least a portionof the first hole perimeter. The automated method can also includecutting a second hole feature in the workpiece by cutting a secondlead-in using a third command speed, the third command speed greaterthan the first command speed. The command speed can be increased fromthe third command speed to a fourth command speed after cutting thesecond lead-in to cut at least a portion of the second hole perimeter.In some embodiments, the fourth command speed and the second commandspeed are substantially the same. The automated method can also includecutting the first hole feature in the workpiece using a first secondarygas flow, cutting the second hole feature in the workpiece using asecond secondary gas flow and cutting a contour (e.g., feature 115 or120 of FIG. 3) in the workpiece using a third secondary gas flow havinga higher nitrogen content than the first secondary gas flow or thesecond secondary gas flow. The first secondary gas flow and the secondsecondary gas flow can have substantially the same gas composition.

Another exemplary automated process can be used to cut a plurality(e.g., two or more) hole features (e.g., feature 105 as shown in FIG. 3)in a workpiece. The automated method can include a one or more automatedprocesses used to cut, for example, a first hole feature having a firstdiameter, a second hole feature having a second diameter greater thanthe first diameter, and a contour. For example, the first hole featurecan be cut using a first automated process by initiating a secondary gasflow (e.g., using the system shown in FIG. 5) having a first gascomposition and a first set of cutting parameters. The second holefeature can be cut using a second automated process by initiating thesecondary gas flow having a second gas composition and using a secondset of cutting parameters. At least one parameter of the second set ofcutting parameters can be different from the first set of cuttingparameters (e.g., different lead-in command speeds and/or cuttingspeeds). The contour feature (e.g., features 115 or 120 in FIG. 3) canbe cut using a gas composition with a greater nitrogen content used incutting the hole features. For example, the automated method can includecutting a contour using a third automated process by initiating thesecondary gas flow having a third gas composition, the third gascomposition having a greater nitrogen content than the first and secondgas compositions and using a third set of cutting parameters. At leastone parameter (e.g., a gas composition of the secondary gas) of thethird set of cutting parameters can be different from the first orsecond set of cutting parameters. The first set of cutting parameterscan include a first lead-in command speed, a first perimeter commandspeed and the first gas composition. The second set of cuttingparameters can include a second lead-in command speed, a secondperimeter command speed, and the second gas composition. The third setof cutting parameters can include a contour command speed and the thirdgas composition. The command speed used to cut the contour can begreater than the command speeds used while cutting the hole features(e.g., the first lead-in command speed, the first perimeter commandspeed, the second lead-in command speed and the second perimeter commandspeed). In some embodiments, the first gas composition and the secondgas composition are the same or substantially the same.

In some embodiments, an automated method is used to cut a first holefeature and a second hole feature, the second hole feature larger thanthe first hole feature. An automated method can include moving theplasma arc torch to a first location and cutting the first hole featurein the workpiece by cutting a first lead-in (e.g., a first zone as shownin FIG. 6A) by ramping up a cutting speed up to a first lead-in cuttingspeed, increasing the cutting speed after the first lead-in to cut afirst perimeter (e.g., a second zone as shown in FIG. 6B), initiatingcurrent ramp down after an inner kerf edge of the first perimeter (e.g.,inner kerf edge 200 of second zone 160 shown in FIG. 6B) substantiallyintersects an outer kerf edge of the first lead-in (e.g., outer kerfedge 140 of first zone 110 as shown in FIG. 6A) and maintaining orincreasing the cutting speed until a cutting current is extinguished,the cutting current extinguished at or near where an outer kerf edge ofthe first lead-in substantially joins an outer kerf edge of the firstperimeter (e.g., the “0 degree point” as described in FIG. 6C). Thecurrent ramp down can be initiated during a lead-out of the cut (e.g.,third zone 210 as shown in FIGS. 6C and 11). The method can also includemoving the plasma arc torch to a second location and cutting the secondhole feature in the workpiece by cutting a second lead-in by ramping upthe cutting speed up to a second lead-in cut speed, the second lead-inspeed greater than the first lead-in cut speed, increasing the cuttingspeed after the second lead-in to cut a second perimeter, initiatingcurrent ramp down after an inner kerf edge of the second perimetersubstantially intersects an outer kerf edge of the second lead-in andmaintaining or increasing the cutting speed until the cutting current isextinguished, the cutting current extinguished at or near where an outerkerf edge of the second lead-in joins an outer kerf edge of the secondperimeter. In some embodiments, current ramp down is initiated at apoint along the lead-out that is based, at least in part, on a diameterof the hole being cut (e.g., hole diameter of the first hole feature orthe second hole feature). In some embodiments, the workpiece is piercedto begin cutting each hole feature.

The plasma arc torch system (e.g., the system of FIG. 1) can beconfigured to cut a plurality of hole features and/or contours ofvarying sizes, dimensions, in workpieces of varying thicknesses. Thesystem (e.g., as shown in FIG. 1) can include a plasma arc torch havingan electrode (e.g., electrode 27 of FIG. 2) and a nozzle (e.g., nozzle28 of FIG. 2) for a corresponding current level and a computer numericalcontroller (e.g., CNC 12 of FIG. 1). The CNC can be configured tocontrol cutting parameters for the plasma arc torch. For example, theCNC can select, from a plurality of gas compositions (e.g., thesecondary gas flow composition from an automatic gas control system asshown in FIG. 5), a first secondary gas composition used to cut holefeatures and a second secondary gas composition used to cut contours.The CNC can also select, from a plurality of perimeter cutting speeds, aperimeter cutting speed (e.g., cutting speed and/or a correspondingcommand speed used to cut the second zone as shown in FIG. 6B) based ona material thickness of a workpiece. The CNC can select, from aplurality of lead-in speeds, a lead-in speed (e.g., a cutting speedand/or a corresponding command speed used to cut the first zone as shownin FIG. 6A) based on a size of a hole feature to be cut and the materialthickness of the workpiece, each perimeter cutting speed greater thaneach corresponding lead-in speed. The lead-in speed can be proportionalto the size of the hole feature to be cut. The CNC can be configured toselect, from a plurality of negative time offset values, a negative timeoffset value based on the current level (e.g., cutting current level). Anegative time offset value can be associated with an asynchronous stopcommand. As discussed below, the asynchronous stop command is a commandthat tells the plasma arc torch to extinguish the plasma arc, butcontinue moving the torch head. The negative time offset can be definedas a variable having a value that controls/determines when the plasmaarc torch begins initiation of current ramp down (e.g., current shutdown), while still moving the torch head. A value for the negative timeoffset can be chosen such that the current ramp down begins at a pointso that the current is extinguished by the time the torch head reachesthe “0 degree point” as shown in FIG. 6C. The torch head can continuemoving until the current is extinguished. The negative time offset canbe based on the size of the hole feature to be cut or the current level.

The CNC can be configured to retrieve/read/obtain instructions from acomputer readable product. A computer readable product, tangiblyembodied on an information carrier, and operable on a CNC for cutting aplurality of hole features and/or contour features in a workpiece with aplasma arc torch system. The computer readable product can be loaded onto the CNC and can include instructions being operable to cause the CNCto select a shield gas composition having a nitrogen content lower thanair when cutting a hole. The product can also cause the CNC to establisha lead-in cutting speed (e.g., a cutting speed and/or a correspondingcommand speed to cut the first zone as shown in FIG. 6A) for a holefeature to be cut, the lead-in cutting speed a function of a diameter ofthe hole feature to be cut and establish a perimeter cutting speed(e.g., a cutting speed and/or a corresponding command speed to cut thesecond zone as shown in FIG. 6B) for the hole feature to be cut, theperimeter cutting speed greater than the corresponding lead-in cuttingspeed. The product can also provide a first command (e.g., anasynchronous stop command) to extinguish a plasma arc, the first commandindependent of a second command to decelerate a plasma arc torch. Theperimeter cutting speed can be based on a thickness of the workpiece.

FIGS. 7A-7C show different shapes for the first zone of the path (e.g.,lead-in shapes) that can be used in cutting a hole feature from aworkpiece, according to illustrative embodiments of the invention.Different lead-in shapes can be used to cut a hole feature from aworkpiece. FIG. 7A shows an exemplary straight lead-in shape 110A forcutting a hole feature. FIG. 7B shows an exemplary quarter circle 110Blead-in shape for cutting a hole feature. FIG. 7C shows an exemplarysemi-circle lead-in shape 110C for cutting a hole feature.

FIGS. 8A-8D show the results of hole features cut from a workpiece usinga semi-circle shaped path in the first zone (e.g., semi circle lead-in)and a hole feature cut from a straight path in the first zone (e.g., astraight lead-in). FIGS. 8A-8D show “transition” points 400A-D where theend 230 of the third zone 210 substantially intersects the beginning 170of the second zone 160 (e.g., where lead-in of the cut meets theperimeter of the cut and the kerf break-in region (e.g., “lead-out”) ofthe cut). FIG. 8A shows a top view of a hole feature cut from aworkpiece using a straight shape for the first zone of the path (e.g.,110A of FIG. 7A). FIG. 8B shows a bottom view of the hole feature ofFIG. 8A. FIG. 8C shows a top view of a hole feature using a semi-circlelead-in shape (e.g., 110C of FIG. 7C). FIG. 8D shows a bottom view ofthe hole feature cut from a workpiece of FIG. 8C. As shown in FIGS.8A-8B, a hole feature cut using a straight-shaped first zone (e.g., astraight lead-in or 110A of FIG. 8A) resulted in unwanted defects, suchas a protrusion. As shown in FIGS. 8C-8D, a hole feature cut using afirst zone shaped like a semi-circle 110C (e.g., a semi-circle lead-in)generated a hole feature with less defects than the hole feature cutusing a straight lead-in.

FIG. 9 is a graph showing measured deviations for different lead-incommand speeds, according to illustrative embodiments of the invention.The graph shows measurements of deviations in the hole feature in thetransition area where the first zone, second zone and third zone asshown in FIGS. 6A-6C merge. The graph shows deviations (“D leveldeviations”) for different “lead-in speeds” (e.g., command speed set forcutting along the first zone as shown in FIG. 6A). Specifically, thegraph shows “D level deviations” which are deviations measured in thehole feature +90 degrees counterclockwise from the “0 degree point” 270and −90 degrees clockwise from the “0 degree point” 270 as shown inFIGS. 6C-6D. The “0.000” line is where the hole should be if the holewere a “perfect” hole free of defects/deviations. Points above and belowthe “0.000 line” indicate deviations/defects such as protrusions anddivots, respectively. There are smaller deviations/defects at the −90degree point and +90 degree point and greater deviations/defects nearthe “0 degree point” (e.g., point 270 in FIGS. 6C-6D). As compared tocylindricity (as described above for FIG. 4), which encompasses thethickness and the perimeter of the hole feature, the deviations in FIG.9 reflect a segment/portion of the hole feature at a given depth. Whileit can be desirable for the lead-in speed (e.g., command speed for thefirst zone of the path) to be less than the speed for cutting theperimeter of the hole (e.g., the command speed for the second zone ofthe path), there exists an optimal speed for the hole feature.Optimizing the lead-in speed can further reduce deviations (e.g., divotsor protrusions) at positive angles (e.g., in the second zone where thefirst zone transitions into the beginning of the second zone).

A method to measure deviations in the hole feature can include the stepof scanning, at a depth near the bottom of the hole, a half circle ofthe hole feature away from the lead-in and arc shut off region (e.g.,scanning a portion of the second zone/perimeter of the hole, forexample, clockwise from the −90 degree point to the +90 degree point orcounterclockwise from the +90 degree point to the −90 degree point asshown in FIGS. 6A-6D) to determine the hole diameter and centerlocation. The method can include a second step of scanning, at about thesame depth, the lead-in and arc shut off region of the hole (e.g.,scanning the third zone and the beginning of the second zone, forexample, clockwise from the +90 degree point to the −90 degree point orcounterclockwise from the −90 degree point to the +90 degree point asshown in FIGS. 6A-6D) and calculate deviations from the measured holediameter and location (e.g., by comparing the measurements obtained byscanning away from the lead-in and arc shut off region with themeasurements obtained by scanning the lead-in and arc shut off region).As noted above the current can be extinguished at or substantially nearthe “0 degree point” 270 (e.g., where the outer kerf edge of the firstzone intersects with the outer kerf edge of the third zone as shown inFIGS. 6C-6D), thus defining the “arc shut off region.” The deviationdata can be plotted at each angular position. To determine the optimalprocess for cutting a hole feature, the lead-in speed having minimaldefects (e.g., deviation values closest to zero) in the region can beselected for each hole size.

FIG. 9 is a deviation plot for various lead-in speeds (e.g., variousspeeds for the first zone of the path as shown in FIG. 6A). The holeswere 0.394 inch diameter holes cut from ⅜″ Mild Steel using a cuttingcurrent of 130 amperes and a gas composition of O2/O2 (plasma gas/shieldgas). A cutting speed for the perimeter (e.g., second zone in FIG. 6B)of the hole feature was set at about 45 ipm. The optimal lead-in speedfor this process, material and hole size were speeds set at about 25-27ipm (plots 440 & 450). For example, hole features cut from a lead-inspeed set at about 40 ipm (plot 480) produced greater defects (i.e.,protrusions measured at about 0.023 inches) than holes cut from a cutlead-in speed set at about 25-27 ipm. Hole features cut from a lead-inspeed set at about 20 ipm (plot 410) produced greater defects (i.e.,divots measured at about −0.013 inches) than holes cut from a cutlead-in speed set at about 25-27 ipm. In contrast, hole features cut atlead-in speeds of about 25-27 ipm produced protrusions (e.g., in portionof the second zone defined clockwise from the +90 degree to the 0 degreepoint) measured at about 0 inches to about 0.002 inches.

Typically, the optimal lead-in speeds are reduced as the hole diametergets smaller. A plot of optimal lead-in speed as a function of holediameter could be tested, similar to the plot shown in FIG. 9, developedand curve fit to an equation. The coefficients for the equation couldappear in the hole cut chart which could be read and used in thecalculations performed by the CNC. FIG. 10 is an exemplary look-up chart570 for lead-in command speeds, according to an illustrative embodimentof the invention. As shown in FIG. 10, the optimal lead-in speed can bea function of hole diameter and can vary based on the cutting currentlevel and thickness of the workpiece. The size of the hole feature canbe directly related to the magnitude of the lead-in speed. For example,smaller hole features can be cut using lower lead-in speeds and largerhole features can be cut using greater lead-in speeds. For example, aprocess for cutting a 0.276 inch diameter hole feature from a 0.375 inchmild steel workpiece at 130 Amps can have an optimal lead-in speed setat about 12 ipm to minimize defects in the hole feature. In contrast, aprocess for cutting a 0.315 inch diameter hole feature from a 0.375 inchmild steel workpiece at 130 Amps can have an optimal lead-in speed setat about 19 ipm to minimize defects in the hole feature.

FIG. 11 shows a third zone for a path used in cutting a hole featurefrom a workpiece, according to an illustrative embodiment of theinvention. The motion of the torch head can follow path 210. The thirdzone can extend from a point where the outer kerf edge 140 of the firstzone 110 (e.g., the lead-in of the cut) intersects with an inner kerfedge 200 of the second zone 160 to the “0 degree point” 270 (e.g., wherethe outer kerf edge 140 of the first zone 110 merges with the outer kerfedge 250 of the third zone 210). As noted above, this is anapproximation as the leading edge 261 of the cut will intersect theouter kerf edge of the first zone before the inner kerf edge 200 of thesecond zone 160 intersects. When the torch angular position (Φ) 580while cutting the hole reaches Φref, the kerf leading edge breaks intothe lead-in (e.g., first zone) outer kerf edge 140, approximately wherethird zone 210 begins. As Φ 580 decreases, the amount of materialremaining decreases reaching zero at Φ=0 (“0 degree point”). Theremaining material (e.g., the “diminishing material” 590) can becalculated as a function of Φ.

The diminishing material 590 can be the leftover material from theworkpiece to be cut once the torch head reaches the beginning 220 of thethird zone 210. The diminishing material 590 can be defined at least inpart by an outer kerf edge 140 of the cut in the first zone 110 and anouter kerf edge 250 of the cut in the third zone 210. Removing too muchmaterial can cause divots in the hole feature, while not removing enoughmaterial can cause protrusions in the hole feature. Therefore, it isdesirable to optimize the material removed in the third zone 210 so thatan outer kerf edge 250 of the cut in the third zone 210 substantiallyaligns with an outer kerf edge 180 of the cut in the second zone 160. Asthe amount of remaining material to be removed (e.g., the diminishingmaterial 590) to cut the hole feature varies along the third zone 210(e.g., from the beginning 220 of the third zone 210 to the end 230 ofthe third zone 210 where the first zone 110, second zone 160, and thirdzone 210 substantially intersect), the current density used to cut theworkpiece as the torch travels along the third zone 210 can be optimizedso that the correct amount of material is removed from the workpiece. Aramp down of the cutting current (e.g., the third cutting current)and/or varying the torch speed (e.g., the cutting speed) can beoptimized to provide the desired amount of current density per lineardistance of the travel by the torch in the third zone 210. A cuttingcurrent can be ramped in the third zone 210 to remove a diminishingmaterial 590 such that an outer kerf edge 250 of the cut in the thirdzone 210 substantially aligns with an outer kerf edge 180 of the cut inthe second zone 160. The method can also include substantiallymaintaining or increasing a torch speed in the third zone 210 until thetorch head passes from the third zone 210 into a location correspondingto the second zone (e.g., zone 240 shown in FIG. 6C).

FIG. 12 is a graph 600 showing a cutting current and a command speed asa function of time, according to an illustrative embodiment of theinvention. The process current 610 can be signaled 620 (e.g., by a CNC)to ramp down and extinguish at or substantially near the “0 degreepoint” 270′ (e.g., where the outer kerf edge 140 of the first zone 110merges with the outer kerf edge 250 of the third zone 210 as shown inFIG. 6C and FIG. 11). There can be a propagation delay 630 between whenthe signal 620 to ramp down the current is sent and when the currentlevel actually begins to ramp down. The torch speed 640 (e.g., the torchspeed) can be decelerated after the torch head passes the “0 degreepoint” 270′ and after the current has been extinguished (e.g., after thecutting current reaches substantially zero amperes).

At least one of a plurality of cutting current ramp down operations forcutting in the third zone can be selected, where each of the pluralityof cutting current ramp down operations can be a function of a diameterof the hole feature. The cutting current can be ramped down at a firstpoint in the third zone 210′ (e.g., at or near the beginning of thethird zone) such that the cutting current 610 is extinguished at orsubstantially near a second point 270′ (e.g. corresponding to point 270as shown in FIGS. 6C-6D) in the third zone 210 where the first zone, thesecond zone and the third zone 210′ substantially intersect (e.g., nearthe end 230′ of the third zone 210′). The first point in the third zonecan be determined/calculated using a ramp down time of the cuttingcurrent. The plasma arc torch can be decelerated so that a torch speedreaches substantially zero at a predetermined distance 650 (e.g., ¼″)after the second point 270′.

The process current 610 ramp down and shut off in the third zone 210′can be performed at full process cutting speed (e.g., by substantiallymaintaining the command speed) or at a higher torch speed than thesecond zone (e.g., by increasing the command speed). The current shutoff 610 can be substantially coincident with the 0 degree mark 270(e.g., the lead-in/hole transition location or location where the firstzone transitions into the second zone). In some embodiments, the torchhead can be decelerated 640 to a stop at a predetermined distance 650(e.g., ¼ of an inch) after the “0 degree mark” 270′ equal to or greaterthan the minimum “lead-out” motion length (as described above). Theplasma can be signaled 620 to ramp down at a point in time correspondingto the current ramp down time and propagation delay so that the currentis extinguished when the torch reaches at or near the “0 degree point”270. Therefore, the time interval between the point where the plasmacurrent is signaled 620 to ramp down and the point 270 where the currentis extinguished can correspond to the ramp down time.

In some embodiments, a first command (e.g., the asynchronous stopcommand) is established to extinguish a plasma arc at a first locationalong a cut (e.g., the “0 degree point” 270 of FIG. 6C and 270′ of FIG.12), the first command independent of a second command to vary a motionof the plasma arc torch. The automated process can also includeestablishing a negative time offset associated with the first commandthat determines initiation of a current ramp down at a second location651 that precedes the first location (e.g., zero degree point 270′)along the cut. The negative time offset can be a variable thatdetermines when the plasma arc torch system initiates current ramp down.The value of the negative time offset can be chosen such that initiationof current ramp down begins when the torch reaches the second locationand the current is extinguished when the time the torch reaches thefirst location. In some embodiments, the first location 651 correspondsto an intersection between an outer kerf edge (e.g., edge 190 of FIG.11) of a perimeter of the hole feature being cut and an outer kerf edge(e.g., edge 140 of FIG. 11) of a lead-in of the hole feature being cut.Varying the motion of the plasma arc torch can include decelerating oraccelerating the plasma arc torch. The negative time offset can be thesum of a delay 630 between the first command and initiation of thecurrent ramp down and a time between initiation of the current ramp downand extinguishment of the plasma arc 610. In some embodiments, anegative time offset is retrieved from a cut chart (e.g., chart 660 ofFIG. 13 as shown below). The negative time offset can be a function of adiameter of the hole feature being cut or a current level. Where aplurality of hole features are cut, the techniques as described hereincan be performed for each hole feature being cut.

FIG. 13 is an exemplary look-up chart 660 for cutting parameters,according to an illustrative embodiment of the invention. The ramp downtime of the current can be included in the cut chart 660. The currentramp down time can vary depending on the current level of the process.By way of example, a process operating with a current level of 400A cantake about 250 ms to ramp down (e.g., to extinguish the current). Aprocess operating with a current level of about 50 Amps can take about50 ms to ramp down. Therefore, to extinguish the current at the “0degree point” (e.g., where the outer kerf edge of the first zone mergeswith the outer kerf edge of the third zone as shown in FIG. 6C and FIG.11), the CNC can signal the plasma arc torch system to ramp down thecurrent to extinguish the current at a point based, at least, on acommand speed and the ramp down time (e.g., the time taken for thecurrent to be extinguished).

A minimum deceleration time can be defined as the minimum time that canbe set for a plasma arc torch to decelerate to a stop, so that theplasma arc torch does not begin to decelerate until the arc isextinguished and the torch reaches the “0 degree point” as describedabove in FIGS. 6C-6D. The minimum deceleration time can be calculated byusing an upper limit for the torch head speed (e.g., an 80 Amp processon a ¼″ Mild Steel workpiece can use a cut speed of about 55 ipm) and alower limit for the table deceleration (e.g., a “slow table” can have atable deceleration of about 5 mG). EQN. 1 above can be used to calculatethe minimum lead-out motion length “L” (e.g., the minimum distance thatcan be set so that the table does not begin decelerating until after thecurrent has been extinguished and/or after the torch head hassubstantially reached the “0 degree point,” the minimum distancecalculated for a fast torch speed and slow table) which can be about0.25 inches given a torch speed of about 55 ipm and a table decelerationof about 5 mG. Therefore, for most processes, a plasma arc torch can becommanded to decelerate to a stop 0.25 inches after the “0 degree point”so that the plasma arc torch maintains the torch head speed until thecurrent is extinguished. A process with a lower speed (e.g., a slowertorch speed) and/or or a faster table (e.g., a greater tabledeceleration) will come to a stop before it reaches 0.25 inches afterthe “0 degree point” but the table will still decelerate after thecurrent has been extinguished. In an alternative embodiment, the CNCnegative cut off time to decelerate the torch head (e.g., to a stop) canbe set to the sum of the propagation delay 630, process ramp down 610(e.g., the time taken to ramp down the current), any additional lead-outand motion deceleration times 650.

As described above in FIG. 9, FIG. 14 shows measurements of deviationsin the hole feature in the transition area where the first zone, secondzone and third zone as shown in FIGS. 6A-6C merge. Specifically, thegraphs show deviations in the hole feature +90 degrees counterclockwisefrom the “0 degree point” and −90 degrees clockwise from the “0 degreepoint” as shown in FIGS. 6A-6D. Graph 670 shows measured deviations fora hole feature, according to an illustrative embodiment of theinvention. Plot 661 shows the outer kerf edge of the first zone, asshown in FIG. 6A. To minimize the depth of the lead-in/lead-out formerror “ding” and/or “divot”, the process ramp down (e.g., ramping downon the current in the third zone as shown in FIGS. 6C and 12) can beperformed by substantially maintaining or increasing the full processcutting speed (e.g., increasing the cutting speed by setting a highercommand speed). The average deviation (e.g., divot) produced in thethird zone (e.g., between −90 degrees and 0 degrees as shown in FIG. 6C)for the holes was about −0.020 inches.

FIG. 15 shows an automated method for operating a plasma arc torch tocut a hole feature from a workpiece, according to an illustrativeembodiment of the invention. Software can generate code for the CNC toexecute and instruct the plasma system to perform a number of stepsduring operation of the torch. A step can include locking out heightcontrol for the plasma arc torch (step 800). The gas composition (e.g.,O2/O2 for plasma/shield gas) can be set from the lookup chart (step810). The kerf value (e.g., from a lookup chart) can be used tocalculate the motion diameter from the hole feature diameter to be cut(step 820). A step can include reading/setting the command speed fromvalues in the hole cut chart (step 830). The path used to cut the holefeature can be programmed to include a 360 degree arc, an asynchronousstop command, and a lead-out arc length (e.g., an arc in the fourth zoneas shown in FIG. 6D) (step 850). The asynchronous stop command can be acommand that tells the plasma arc torch to extinguish the plasma arc,but to continue moving the torch head. The torch stop command (e.g., thecommand to decelerate the torch to a stop) can then be given later. Theasynchronous stop command can be inserted at the “0 degree point” (e.g.,point 270 as shown in FIGS. 6C-6D) and can include an offset with a timeinterval (e.g., a negative time offset) that corresponds to the rampdown time so that the current is extinguished to substantially zero atthe “0 degree point” (Step 840). The lead-out arc length can beprogrammed to correspond to the minimum lead-out motion length (e.g., asdescribed above in EQN. 1), so that the torch does not begin todecelerate until after the “0 degree point” (e.g., so that the torchspeed is not lowered until the current is extinguished). A lead-in shape(e.g., a semi-circle) from the hole center to the motion diameter (step860) can be programmed. A lead-in speed can be read/set from values inthe hole cut chart (e.g., command speeds for the first zone as describedabove) (step 870). The current ramp down time can be read from a look uptable for any number of holes sizes and any significant propagationdelay can be added to the time interval that offsets the asynchronousstop command as described above. Thus, an appropriate current ramp downtime can be calculated for any number of hole sizes.

In some embodiments, the automated method includes cutting a pluralityof hole features in a workpiece. The methods as described above can beused to cut each hole feature. Step 840 as described above, can includeestablishing a first location corresponding to where an outer kerf edgeof a cut along a perimeter of each hole feature substantially joins theouter kerf edge of the cut along a lead-in of each hole feature (e.g.,“0 degree point” 270 of FIG. 6C and 270′ of FIG. 12). The method canalso include establishing a second location (e.g., location 651 of FIG.12) preceding the first location based on a hole diameter of the holefeature being cut or a cutting current level and initiating plasma arctermination at the second location such that the plasma arc issubstantially extinguished when the plasma arc torch reaches the firstlocation. The second location corresponding to initiation of currentramp down can be located along a lead-out of a cut (e.g., third zone 210as shown in FIG. 6C and FIG. 11). In some embodiments, a plurality ofhole features having different hole diameters are cut in a workpiecewith a given thickness and a distance traveled by the plasma arc torchfrom the second location to the first location is substantially similar(e.g., the same) for the plurality of hole features. The automatedmethod can also include determining a negative time offset based on thehole diameter of the hole feature being cut, the negative time offsetdetermining initiation of plasma arc termination at the second location.The plurality of hole features having the plurality of hole diameterscan be cut using one set of consumables for the plasma arc torch (e.g.,automated process to cut the hole features without changing theconsumables in the plasma torch). In some embodiments, the workpiece canbe pierced to begin cutting each hole feature.

FIG. 16 is a graph comparing hole quality results for holes cut fromdifferent processes. The graph shows the cylindricity for hole featurescut using different cutting processes 880-920. Cylindricity can be afunction of hole size (e.g., hole diameter). The hole features cut usingprocesses 880-920 in FIG. 16 were each 0.394 inches in diameter, andwere cut in ⅜″ thick mild steel workpieces. Processes 900-910 are holefeatures cut from processes incorporating exemplary features of theembodiments of the invention described herein. Process 920 was a holefeature cut using a laser cutting system. While laser cutting systemshave previously yielded higher quality holes (e.g., comparing Process920 to, for example, Process 880), plasma arc torch systems are lower incost. Therefore, there is a need for high quality holes cut from plasmaarc torch systems.

The plot for Process 880 (“Benchmark Plasma”) shows the cylindricity fora hole feature cut from existing methods. The gas composition forProcess 880 used O₂ plasma gas and Air for shield gas. A straightlead-in (e.g., straight cut for the first zone) was used and the torchwas decelerated prior to the “0 degree point” (e.g., prior toextinguishing the current). The cylindricity for the hole feature cutfrom Process 880 was about 0.059 inches.

The plot for Process 890 (“Partial A”) shows the cylindricity for a holefeature cut where the only change from Process 880 was the gascomposition. The gas composition for Process 890 was O₂ plasma gas andO₂ shield gas. The cylindricity for the hole feature cut from Process890 was about 0.100 inches. Therefore, merely changing the shield gascomposition and flow rate from Process 880 amplified the defects in thehole feature.

The plot for Process 900 (“Partial B”) shows the cylindricity for a holefeature where a semi-circle shape was used to cut the first zone (e.g.,a semicircle lead in) and where the command speeds for the second zonewere higher than the command speed for the first zone. The torch,however, was decelerated before the current was extinguished (e.g.,before the “0 degree point” as shown in FIGS. 6C-6D). The gascomposition for Process 900 was O₂ plasma gas and O₂ shield gas. Thecylindricity for the hole feature cut from Process 900 was about 0.039inches. Therefore, this data shows that changing the command speedsalong the cut and choosing a semi-circle lead-in improved the holequality. A hole cut feature cut by this process has a lower cylindricitythan a hole cut by using a process that has a straight lead-in and notorch speed change between the first and second zones.

The plot for Process 910 (“Full Solution”) shows the cylindricity for ahole feature where a semi-circle shape was used to cut the first zone,where the command speeds for the second zone were higher than thecommand speed for the first zone and where the torch was deceleratedafter the current was extinguished (e.g., after the “0 degree point” asdescribed above). The gas composition for Process 910 was O₂ plasma gasand O₂ shield gas. The cylindricity for the hole feature cut fromProcess 910 was about 0.020 inches, thereby showing improvement in cutquality as compared to the other plasma arc torch processes. A holefeature cut by this process has a lower cylindricity than a hole featurecut by a torch that was decelerated before the current was extinguished.

The plot for Process 920 (“Laser”) shows the cylindricity for a holefeature cut using a laser cutting system. The cylindricity for the holefeature cut from a laser system was about 0.015 inches. Cutting a holefeature incorporating the aspects/features of the embodiments describedherein, as shown in plots for Processes 900-910, improved the quality ofholes cut using plasma arc torch systems.

FIG. 17 is a flow chart depicting how a processor, such as acomputerized numeric controller (e.g., CNC 12 of FIG. 5), can be used tomanipulate gas flows to implement principles of the invention. FIG. 17shows flow operations that can be contained within a computer readableproduct which is embodied in an information carrier, according to anillustrative embodiment of the invention. Other embodiments are alsowithin the scope of the invention. As shown in FIG. 17, a CAD filecontaining the part to be cut is provided to the CNC 1510, or nestingsoftware, and based on instructions contained in the cut chart the CNCselects the shield gas composition. In another embodiment, instructionscontained in the nesting software determine the shield gas composition.In some embodiments, once the CNC uses the computer readableinstructions to determine if a hole feature or contour is being cut, thetorch is powered on 1520 and the arc is transferred to the workpiece1530. When the arc is initiated, the initiation shield and plasma gas isused, for example the combinations shown below in FIG. 18. After the arcis transferred to the workpiece, the torch is lowered to the workpieceand the arc pierces the workpiece 1540. In one embodiment, the arcpierces the workpiece using air as the pierce shield gas. Once thepierce step is completed, the CNC uses the computer readableinstructions to select the appropriate shield gas depending on whether ahole feature or a contour is to be cut. In some embodiments, thedetermination as to whether a hole feature or a contour is to be cut(and selection of the appropriate shield gas composition) is based on anexamination of the dimensions of the hole in relation to the thicknessof the workpiece. In one embodiment, if the diameter of the feature isabout 2.5 times or less than the thickness of the workpiece, then asmall internal feature (e.g., hole feature) is to be cut, and the CNCselects the second shield gas 1550. In some embodiments the shield gascomposition selected for hole feature cutting is O₂; and in someembodiments the shield gas composition is O₂, He, N₂, or a combinationthereof In some embodiments, the instructions regarding the shield gascompositions are included in the instructions on the cut chart. Once thesecond shield gas is selected, the CNC will control the shield gas flowsuch that the second shield gas composition flows through the shield gassupply lines. The hole feature is then cut 1560 in the workpiece usingthe second shield gas composition as determined by the instructionscontained in the cut chart, or designated by the nesting software. Afterone or more hole features are cut in the workpiece, the CNC initiatesthe contour cutting operations 1570.

When the CNC initiates the contour cutting operation, the arc is againinitiated 1530 using the initiation shield and plasma gas for contourcutting. The arc then pierces the workpiece 1540, and as the contourcutting begins, the CNC selects the first shield gas for the contourcutting operation 1580. If it is determined that a contour is being cut,then the CNC selects the first shield gas composition for the contourcut 1580. The identification of a contour can be selected based on theshape of the cut or in the case of an internal feature, it may be basedon a ratio of the diameter of the opening to be cut to the thickness theworkpiece. In some embodiments when cutting a contour, the arcinitiation, the piercing of the workpiece, and the contour cut are allperformed using a single shield gas composition, that is, the firstshield gas composition. In some embodiments, the shield gas during thearc initiation and the piercing of the workpiece is different than theshield gas used when cutting the contour shape in the workpiece. Whencutting a hole feature or contour in a workpiece, the same operationalsteps can be followed, although different shield gas compositions may beselected for each step.

FIG. 18 is a table illustrating examples of gas combinations that can beused with an embodiment of the invention. In one embodiment, the gasesare selected to provide optimal gas cutting properties based upon theplasma torch operation to be performed, such as hole feature cutting orcontour cutting. The exemplary gas compositions shown in FIG. 18 are formild steel cutting applications, although other material workpieces canbe cut using different shield gas compositions that are better suitedfor such materials. In some embodiments, a mixture of He and N₂ can beused in place of oxygen for the hole feature shield gas cuttingstainless steel or aluminum.

In the embodiment demonstrated in FIG. 18, while cutting either acontour or a hole feature, the system provides air as the plasma gas andthe shield gas during plasma arc initiation. Air is used as the plasmagas because it tends to provide better consumable life compared to O₂during arc initiation. Once the arc is initiated and transferred to theworkpiece, the plasma gas is changed to O₂ and the shield gas remains asair for the piercing process. In this instance, the plasma gas isswitched to the gas that is appropriate for the nozzle design, in thisembodiment O₂, in order to prevent damage to the nozzle as the currentis ramped up to the cutting current. In most cases it is desirable thatthe cutting gas be present at the time full cutting current is reached.The shield gas for the piercing process, on the other hand, remains asair. Air shield gas for piercing operations has been shown to leave asmaller pierce penetration which limits waste in the workpiece. Once theworkpiece is pierced, the plasma torch will begin cutting along the edgeof the penetration with the motion of the torch. In piercing, the torchis generally stationary and the object is to make a penetrationcompletely through the workpiece. Cutting, on the other hand, involvedmoving the torch by severing exposed edges to create the desired shape.

Referring again to the table of FIG. 18, after the piercing step, theshield gas can be selected based upon the type of cut: a contour or ahole feature. In cutting a contour, the shield and plasma gas remainunchanged. The combination of O₂ plasma gas and air shield gas allowsstraight dross free edges and fast cut speeds (e.g., cut speeds orcommand speeds) when cutting contours using an O₂ plasma gas and airshield gas combination, however, tends to create a hole feature with alarge degree of taper or bevel, creating a poor quality hole feature. Bykeeping O₂ as the plasma gas and switching the shield gas also to O₂when cutting hole features or small internal features, the taper of thehole feature can be reduced if not eliminated. Taper is reduced by usingan O₂ shield gas when cutting mild steel compared to air because theamount of nitrogen in the shield gas is reduced. Thus, other gases orgas compositions with low nitrogen content could be used in theembodiment in FIG. 18. In other embodiments, a shield gas with differentcomposition combinations can be used when cutting hole features.

FIG. 19A is an example of a cross sections of a hole cut using prior artcutting processes (e.g., using the same shield gas composition for botha contour cut and a hole feature cut in the same workpiece). In FIG. 19Athe cylindricity (“taper” or “bevel”) of the hole can be measured byforming concentric cylinders with a diameter equal to the diametermeasurement at the top 71, middle 72, and bottom 73 of the edge 74 ofthe hole. The greatest difference between the diameters is illustratedby the space between the arrows 81. The large difference between theradiuses of the two datum cylinders in FIG. 19A indicates a poor qualityhole. Such holes can require significant post cutting treatment.

FIG. 19B is a cross section of a hole feature cut with an embodiment ofthe present invention incorporating the exemplary techniques asdescribed above. The cylindricity (“taper” or “bevel”) of the hole canbe measured also by forming concentric cylinders with a diameter equalto the diameter measurement at the top 71, middle 72, and bottom 73 ofthe edge 74 of the hole. In FIG. 19B, it can be seen that the bevel ortaper of the edge of the hole cut is significantly reduced as comparedto the bevel of the hole edge in FIG. 19A (e.g., see also FIG. 3).Further, the reduced cylindricity can also be seen by the reduceddistance between the arrows 81 as compared to FIG. 19A. With the reducedbevel or taper of the edges of the hole, the cylindricity tolerance zonebetween the two concentric cylinders is minimal and resulting in a muchhigher quality hole, requiring no post cutting treatment.

The above-described techniques can be implemented in digital electroniccircuitry, or in computer hardware, firmware, software, or incombinations of them. The implementation can be as a computer programproduct, i.e., a computer program tangibly embodied in an informationcarrier (e.g., a CPS). An information carrier can be a machine-readablestorage device or in a propagated signal, for execution by, or tocontrol the operation of, data processing apparatus (e.g., aprogrammable processor, a computer, or multiple computers).

A computer program (e.g., a computer program system) can be written inany form of programming language, including compiled or interpretedlanguages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment. A computer program can bedeployed to be executed on one computer or on multiple computers at onesite or distributed across multiple sites and interconnected by acommunication network.

Method steps can be performed by one or more programmable processorsexecuting a computer program to perform functions of the invention byoperating on input data and generating output. Method steps can also beperformed by, and apparatus can be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit). Modules can refer to portionsof the computer program and/or the processor/special circuitry thatimplements that functionality.

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read-only memory ora random access memory or both. The essential elements of a computer area processor for executing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, (e.g.,magnetic, magneto-optical disks, or optical disks). Data transmissionand instructions can also occur over a communications network.Information carriers suitable for embodying computer programinstructions and data include all forms of non-volatile memory,including by way of example semiconductor memory devices, e.g., EPROM,EEPROM, and flash memory devices; magnetic disks, e.g., internal harddisks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROMdisks. The processor and the memory can be supplemented by, orincorporated in special purpose logic circuitry.

To provide for interaction with a user, the above described techniquescan be implemented on a computer having a display device, e.g., a CRT(cathode ray tube) or LCD (liquid crystal display) monitor, fordisplaying information to the user and a keyboard and a pointing device,e.g., a mouse or a trackball, by which the user can provide input to thecomputer (e.g., interact with a user interface element). Other kinds ofdevices can be used to provide for interaction with a user as well; forexample, feedback provided to the user can be any form of sensoryfeedback, e.g., visual feedback, auditory feedback, or tactile feedback;and input from the user can be received in any form, including acoustic,speech, or tactile input.

The above described techniques can be implemented in a distributedcomputing system that includes a back-end component, e.g., as a dataserver, and/or a middleware component, e.g., an application server,and/or a front-end component, e.g., a client computer having a graphicaluser interface and/or a Web browser through which a user can interactwith an example implementation, or any combination of such back-end,middleware, or front-end components. The components of the system can beinterconnected by any form or medium of digital data communication,e.g., a communication network. Examples of communication networksinclude a local area network (“LAN”) and a wide area network (“WAN”),e.g., the Internet, and include both wired and wireless networks.

Comprise, include, and/or plural forms of each are open ended andinclude the listed parts and can include additional parts that are notlisted. And/or is open ended and includes one or more of the listedparts and combinations of the listed parts.

While the invention has been particularly shown and described withreference to specific illustrative embodiments, it should be understoodthat various changes in form and detail may be made without departingfrom the spirit and scope of the invention.

The invention claimed is:
 1. An automated method for cutting a pluralityof hole features in a part in a workpiece with a plasma arc torch whileusing a single plasma torch consumable configuration, the methodcomprising: cutting a first hole feature in the part, the first holefeature having a first diameter, and the first hole feature being cutusing a first automated process comprising: initiating a secondary gasflow having a first gas composition; and cutting the first hole featurewith a first set of cutting parameters comprising a first lead-incommand speed; cutting a second hole feature in the part, the secondhole feature having a second diameter that is different than the firstdiameter of the first hole, and the second hole feature being cut usinga second automated process comprising: initiating the secondary gas flowhaving a second gas composition; and cutting the second hole featurewith a second set of cutting parameters comprising a second lead-incommand speed, wherein the second lead-in command speed is differentfrom the first lead-in command speed.
 2. The automated method of claim1, wherein: the first set of cutting parameters further includes a firstperimeter command speed and the first gas composition; the second set ofcutting parameters further includes a second perimeter command speed,and the second gas composition; and the first perimeter command speed isthe same as the second perimeter command speed; or the first gascomposition is different from the second gas composition.
 3. Theautomated method of claim 1 further comprising: cutting a contour usinga third automated process by: initiating the secondary gas flow having athird gas composition, the third gas composition having a greaternitrogen content than the first and second gas compositions; and cuttingthe contour with a third set of cutting parameters, wherein at least oneparameter of the third set of cutting parameters is different from thefirst or second set of cutting parameters.
 4. The automated method ofclaim 1, wherein the first gas composition and the second gascomposition are substantially the same.
 5. The automated method of claim1 wherein: cutting the first hole feature with the first set of cuttingparameters includes: moving the plasma arc torch to a first location;cutting a first lead-in by ramping up a cutting speed up to the firstlead-in command speed; increasing the cutting speed after the firstlead-in to cut a first perimeter; initiating current ramp down after aninner kerf edge of the first perimeter substantially intersects an outerkerf edge of the first lead-in; and maintaining or increasing thecutting speed until a cutting current is extinguished, wherein thecutting current is extinguished at or near where an outer kerf edge ofthe first lead-in substantially joins an outer kerf edge of the firstperimeter; cutting the second hole feature with the second set ofcutting parameters includes: moving the plasma arc torch to a secondlocation; cutting a second lead-in by ramping up the cutting speed up tothe second lead-in command speed, the second lead-in command speed beinggreater than the first lead-in command speed; increasing the cuttingspeed after the second lead-in to cut a second perimeter; initiatingcurrent ramp down after an inner kerf edge of the second perimetersubstantially intersects an outer kerf edge of the second lead-in; andmaintaining or increasing the cutting speed until the cutting current isextinguished, wherein the cutting current is extinguished at or nearwhere an outer kerf edge of the second lead-in joins an outer kerf edgeof the second perimeter.
 6. The automated method of claim 5 furthercomprising cutting the first hole feature or the second hole feature byinitiating current ramp down at a point based on a diameter of the firsthole feature or the second hole feature.
 7. A plasma arc torch systemfor cutting a plurality of hole features in a workpiece, the plasma arctorch system including a plasma arc torch and a computer numericalcontrol device comprising a non-transitory executable code that whenexecuted by the plasma arc torch system instructs the computer numericalcontrol device to operate the plasma arc torch according to the methodof claim
 1. 8. The automated method of claim 2 further comprising:cutting a contour using a third automated process by: initiating thesecondary gas flow having a third gas composition, the third gascomposition having a greater nitrogen content than the first and secondgas compositions; and cutting the contour with a third set of cuttingparameters, wherein at least one parameter of the third set of cuttingparameters is different from the first or second set of cuttingparameters.
 9. The automated method of claim 8, wherein the third set ofcutting parameters includes a contour command speed and the third gascomposition.
 10. The automated method of claim 9, wherein the contourcommand speed is greater than the first lead-in command speed, the firstperimeter command speed, the second lead-in command speed and the secondperimeter command speed.